In quotes: Timeline of reaction to UK's EU treaty veto
Prime Minister David Cameron 05:13
"I said before coming to Brussels that if I couldn't get adequate safeguards for Britain in a new European treaty then I wouldn't agree to it.
"What is on offer isn't in Britain's interests so I didn't agree to it. Let me explain why this matters.
"Of course we want the eurozone countries to come together and to solve their problems. But we should only allow that to happen inside the European Union treaties if there are proper protections for the single market and for other key British interests.
Without those those safeguards, it is better not to have a treaty within a treaty but to have those countries make their arrangements separately. That is what is now going to happen."
French President Nicolas Sarkozy 06:21
"Our British friends - this is not a criticism - say: 'not only are we not in the euro, but we're glad we're not in it.'
And we, who defend the euro, who are changing the way the euro functions and are learning from the crisis... we're not going to apologise for doing everything we're doing to save our currency."
Foreign Secretary William Hague 07:16
"I don't accept at all the idea of a two speed Europe.
"Within the European Union there are different groups of countries that cooperate on different subjects. Some are in the euro and some aren't.
"It doesn't mean the United Kingdom loses its influence over other matters.
"We are of course - by preventing a new treaty amending the treaties of the European Union - ensuring that the key decisions that affect us such as to do with the single market are still made by the 27 nations - including us."
Shadow Foreign Secretary Douglas Alexander
"I don't glory in Britain's isolation this morning and I regret just how badly David Cameron's negotiation strategy has let Britain down.
"Because if you strip away all the rhetoric and look at the reality, Britain today is more isolated than at any point in the 35 years since we joined the European Community.
"This outcome is a sign not of strength from the Prime Minister, but of profound weakness."
Former Liberal Democrat leader Sir Menzies Campbell
"David Cameron could not have come back without achieving safeguards for the purpose of ensuring that the financial services industry - which is such an important part of our economy - was safeguarded.
"That's why - if there was to be no movement on the side of what I'll characterise as the French - then David Cameron had no option but to reach the conclusion which he did."
Liberal Euro MP Sharon Bowles
"I'm gutted - because we are on the outside and I don't see how being on the outside is in our interests or in the interest of the City of London or any of the things we were allegedly trying to protect.
"Where once we had a powerful voice now even that is challenged."
Liberal Democrat leader Nick Clegg
"Clearly the prime minister and I worked together on the request for the safeguards which we were seeking.
"Let's be clear. We were not seeking some great repatriation of powers from Europe back to Britain, we were not even seeking some great exceptional treatment for the City of London.
"I thought that was reasonable, the prime minister put that forward as a reasonable package.
"It is a pity that other countries chose not to take up that suggestion because that would have allowed us to move together as a club of 27."
Conservative MP Bernard Jenkin
"It is a watershed. But it is the beginning of a long process.
"Ultimately the government may still be faced with demands for a referendum because if the European Union is changing so dramatically when are the British people going to get their say unless we change our terms of membership?"
Business Secretary Vince Cable
"These issues about treaty change and how we deal with it, that's something we're going to have to digest.
"The really important thing about this summit is that the eurozone sorts out its very deep financial crisis because hundreds of thousands of British jobs depend on the eurozone crisis being resolved."
Conservative MP Bill Cash
"The fact that we are now vetoing this treaty means that we are set on a path which involves fundamental renegotiation, make no mistake about it.
"And that in due course will also require a referendum - because it's about the British people, it's about the electors, the people who send us to parliament - it's our job to protect them and it's also our job to protect their democracy."
Labour leader Ed Miliband
"It's a terrible outcome for Britain because we are now going to be excluded from key economic decisions that will affect our country in the future and, frankly, David Cameron has mishandled these negotiations spectacularly.
"And really what he's done is he's spent many months not really promoting the national interest but more interested in dealing with the splits in his own party.
"That has served Britain very badly and I really fear the consequences this will have for our country."
Prime Minister David Cameron
"I think I did the right thing for Britain. We were offered a treaty that didn't have proper safeguards for Britain and I decided it was not right to sign that treaty - that was the decision I took.
"You're obviously in a room with 26 other people who are saying - put aside your national interest go along with the crowd, do what will make life easy and comfortable for you there in that room.
"But you say no. It's important that we get the things that Britain needs and so I decided not to sign that treaty. It's what I said I'd do and it's what I did."
Liberal Democrat Euro MP Chris Davies
"It's all about relationships and what happened at the dinner last night in Brussels was that the seventeen countries in the eurozone gathered amongst the 27 of the European Union and said we need help.
"And David Cameron effectively said, I'm not prepared to help, I'm not prepared to lift a finger. In fact, he went worse than that. He kicked them in the teeth. And that will not be forgotten."
Liberal Democrat deputy leader Simon Hughes
"We are not cheering anything. We are not cheering the fact that we couldn't get an agreement.
"It would have been better to get an agreement. But I know what would not have been in Britain's interests.
"It would not have been in Britain's interests to spend our time in our parliament... being distracted by a referendum about a treaty, which is what the eurosceptics have wanted, that would be absolutely not in our interests."
Liberal Democrat Lord Oakeshott
"He's (David Cameron) playing with fire. It's desperately dangerous to cut ourselves off from our friends and allies in Europe and he's putting millions of jobs all over Britain at risk by his special pleading for special interests in the city and by appeasing the Tory right. "
Justice Secretary Ken Clarke
"I think it's a disappointing, very surprising outcome, there'll be a big statement made by the Prime Minister on Monday where I shall be sitting listening and I shall be discussing what we're going to do now."
Chancellor George Osborne
"We have protected Britain's financial services, and manufacturing companies that need to be able to trade their businesses, their products, into Europe.
"We've protected all these industries from the development of eurozone integration spilling over and affecting the non-euro members of the European Union."
Former Conservative cabinet minister John Redwood
"I am not calling for a referendum today because I'm very strongly in support of what the prime minister did in the last two days and that delays the need for an immediate decision.
"But I think at some point, yes, we need to consult the people again.
"Millions did not have the chance to vote in 1975 because they were too young. And millions who did vote in 1975 were told they were merely voting for a free-trade area, which they were happy to sign up to."
Shadow Financial Secretary Chris Leslie
"He (David Cameron) hasn't vetoed anything, he has been vetoed; the other 26 have turned their back on him and now we're just as subject to all of these risks from all sorts of regulations that they might want to put on the City.
"Who knows what that 26 are going to do because Britain's no longer in the room with them.
"Instead, we're now isolated. This is a very weak decision and it's a negotiation that's failed on multiple levels. Monumental harm for the UK."
Deputy Prime Minister Nick Clegg
"I am bitterly disappointed by the outcome of last week's summit.
"Precisely because I think there is now a real danger that over time the United Kingdom will be isolated and marginalised within the European Union.
"I don't think that is good for jobs in the City or elsewhere. I don't think it is good for growth. I don't think it is good for families up-and-down the country.
"That is why I, as a Liberal Democrat in this coalition government, will now do everything I can to make sure that this set-back does not become a permanent divide, that we get back into the saddle and that we work and exercise leadership on things like the single market, the environment, foreign policy, defence policy, all the things that we need to do at a European level so that Britain leads and we don't end up retreating to the margins."
Former Liberal Democrat leader Paddy Ashdown on Sky News
"In my view almost every other Prime Minister of recent times would have had no difficulty getting this deal through in the interests of Britain.
"But Mr Cameron has spent the past three or four months on the sidelines, lecturing Europe while not being part of it and sometimes that's verged into near insult.
"The eurosceptic anti-European prejudice year after year, supported by many of the newspapers, has now built up an anti-British prejudice in Europe and we're paying a very very high price for that."
Shadow Foreign Secretary Douglas Alexander
"What we have heard from the Deputy Prime Minister this morning is very significant because he's confirmed what as Labour we've been saying for 48 hours, that actually David Cameron secured no additional safeguards when he walked out of the room on Thursday evening.
"Secondly that David Cameron was motivated by party interests not national interest, and thirdly he ended up with a bad deal for Britain.
"Now these are not the words of a Labour spokesman or of commentators, these are the views of the Deputy Prime Minister and that explains the scale of the difficulties facing the coalition."
Defence Secretary Phillip Hammond
"David Cameron did not go to Europe with the intention of wrecking what the Europeans are trying to do.
"He went with a very modest and reasonable set of proposals to make sure that the UK and particularly our single largest industry, the financial services, was not disadvantaged by the proposed new treaty."
Foreign Secretary William Hague on Sky News
"We're not marginalised. I don't agree. I don't use the terminology two-speed Europe.
"That implies that there's one group getting on with something more quickly than another group.
"There are overlapping circles of decision-making in Europe. Some are in the euro; some aren't. Some are in the Schengen border controls; some aren't. "
Labour leader Ed Miliband
"What I say to Liberal Democrats and others is that we will work with anybody who thinks this position can not stand.
"We must find a better way forward for Britain. The prospect of all these other countries meeting without us, making decisions without us is not a position that any of us should accept. "
Conservative Euro MP Daniel Hannan
"We have an absolutely enormous opportunity here if we now stick to our guns.
"If the eurozone is going to go down this road towards more regulation and more union and more uniformity and higher costs, we should be the off-shore haven, we should be the Hong Kong to their China.
"We should be the sanctuary to which people come fleeing the chaos of the eurozone."
Former Labour Foreign Secretary David Miliband
"This is the first veto in history not to stop something. The plans are going right ahead. It was a phantom veto against a phantom threat.
"Fifty-six years ago Anthony Eden walked away from the founding of the European Union and we paid the price for 20 years. This has been an Anthony Eden moment for David Cameron."
Liberal Democrat ex-cabinet minister David Laws
"I think the desirable situation is that Britain would have done a better job before the summit in bringing the other European Union nations on board, in terms of what our objectives were, what we would settle for.
"I think it seems as if many of the other eurozone nations didn't really understand Britain's negotiation position, and it seems to many of us that France took a deliberate decision to ignore the quite reasonable demands of the UK, and perhaps actively seek to exclude the UK from the core of European Union countries.
"And it appears to be France, rather than the UK, which is gloating over the outcome of this summit, which is something that should concern us."
Business Secretary Vince Cable
"The public and the business community are not particularly interested in these tribal arguments.
"I think what we badly need is complete reassurance that we are fully committed to working in the European Union, millions of British jobs depend on it."
Former Labour Business Secretary Lord Mandelson
"The full ramifications of David Cameron's landmark decision to divide Britain from the rest of the EU are sinking in fast.
"As a nation, we are not just set apart in a two-speed Europe but travelling in a different direction.
"If our European partners' sense of despair over us does not abate and if anti-European populism in Britain grows, this could have dramatic consequences for Britain's membership of the EU and, therefore, our economic future."
Former Tory Party chairman Lord Tebbit
"Willingly or unwillingly, the prime minister has now taken the first step towards a solution to the euro mess and a better European structure.
"The British dog has to get out of the federal manger and allow the creation of one or more European republics, composed of countries whose economies and attitudes are sufficiently close to enable them to accept the rough and smooth of a complete political union and a single currency."
London Mayor Boris Johnson
"The reason our brother and sister Europeans are so chronically enraged with the British is that we have been proved completely right about the euro.
"For more than 20 years, British ministers have been coming out to Brussels and saying that they just love all this single-market stuff, but that they doubt the wisdom of trying to create a monetary union.
"And for more than 20 years, some of us have been saying that the reason a monetary union won't work is that you can't do it without a political union - and that a political union is not democratically possible."
Conservative MP David Davis
"He's (Nick Clegg) gone through a 180-degree U-turn, but, surprise, surprise, he leads the Lib Dems."
Asked on the BBC's World at One if there should be an election called, he said no, adding: "They are our political partners and they do bring something important to British politics. I wouldn't want to see them end up having their party meetings in the back of a cab."
Prime Minister David Cameron
"We went seeking a deal at 27 (member states) and I responded to the German and French proposal for treaty change in good faith, genuinely looking to reach an agreement at the level of the whole of the European Union with the necessary safeguards for Britain.
"Those safeguards, on the single market and on financial services, were modest, reasonable and relevant."
Labour Leader Ed Miliband
"The Prime Minister says he had no choice, he did. He could have stayed inside and fought his corner.
"He should have stayed inside and fought his corner. Faced with a choice between the national interest and his party interest he has chosen the party interest.
"We will rue the day this Prime Minister left Britain alone without allies, without influence. It is bad for business, it is bad for jobs. It is bad for Britain."
Labour MP Dennis Skinner
"Is this not the same Prime Minister who month after month has been castigating working people for not staying at meetings to deal with pensions?
"He has walked out, without using his veto; he has walked out, without getting a rebate like Mrs Thatcher; and he has walked out without a couple of opt-outs like Major.
"As Del Boy would say, what a plonker!"
Tory MP Phillip Davies
"The Prime Minister should be in doubt that he did the right thing last week.
"Will he confirm that he will not make any further policy concessions to the lickspittle Eurofanatics on the Lib Dem Benches as a result of doing the right thing for Britain last week?"
Deputy Prime Minister Nick Clegg
"The prime minister and I do not agree on the outcome of the summit last week.
"I made it very clear that I think isolation in Europe, when we are one against 26, is potentially a bad thing for jobs, a bad thing for growth, a bad thing for the livelihoods of millions of people in this country.
"I am not here to defend the European Union in and of itself. I am here to defend the jobs and livelihoods of millions of people in this country.
"That is what I care about. That is why I think what we should do now is build bridges, re-engage and make sure that a British voice is heard in the heart of Europe."