Here is the full text of David Cameron's statement to the House of Commons on the UN resolution authorising a no-fly zone over Libya.
"With permission, Mr Speaker, I would like to make a statement on last night's UN Security Council Resolution.
Mr Speaker, over three weeks ago the people of Libya took to the streets in protest against Colonel Gaddafi and his regime.
There were hopeful signs that a better future awaited them, and that, like people elsewhere in the Middle East and North Africa, they were taking their destiny into their own hands.
Mr Speaker, far from meeting those aspirations, Colonel Gaddafi has responded by attacking his own people.
He has brought the full might of armed forces to bear on them, backed up by mercenaries.
The world has watched as he has brutally crushed his own people.
On the 23rd February the UN Secretary General cited the reported nature and scale of attacks on civilians as "egregious violations of international and human rights law" and called on the government of Libya to "meet its responsibility to protect its people."
He later said that more than 1,000 people had been killed and many more injured in Libya amidst credible and consistent reports of arrests, detention and torture.
Over the weekend of 26th and 27th February, at Britain's instigation, the UN Security Council agreed Resolution 1970.
This condemned Gaddafi's actions.
It imposed a travel ban and assets freeze on those at the top of his regime.
It demanded an end to the violence, access for international human rights monitors and the lifting of restrictions on the media.
And it referred the situation in Libya to the International Criminal Court so its leaders should face the justice they deserve.
Mr Speaker, in my Statement to this House on 28th February, I set out the steps that we would take to implement these measures.
Our consistent approach has been to isolate the Gaddafi regime, deprive it of money, shrink its power and ensure that anyone responsible for abuses in Libya will be held to account.
I also told this House I believed contingency planning should be done for different scenarios including involving military assets, and that this should include plans for a no fly zone.
Mr Speaker, intervening in another country's affairs should not be undertaken save in quite exceptional circumstances.
That is why we've always been clear that preparing for eventualities which might include the use of force - including a no fly zone or other measures to stop humanitarian catastrophe - would require three tests to be met.
Demonstrable need. Regional Support. And a clear legal basis.
First, demonstrable need.
Gaddafi's regime has ignored the demand of the UN Security Council in Resolution 1970, that it stop the violence against the Libyan people.
His forces have attacked peaceful protesters, and are now preparing for a violent assault on a city of a million people that has a history dating back 2,500 years.
They have begun airstrikes in anticipation of what we expect to be a brutal attack using air, land and sea forces.
Gaddafi has publicly promised that every home will be searched and that there will be no mercy and no pity shown.
If we want any sense of what that might mean we only have to look at what happened in Zawiyah where tanks and heavy weaponry were used to smash through a heavily populated town with heavy loss of life.
And we don't have to guess what happens when he has subdued a population.
Human Rights Watch have catalogued the appalling human rights abuses that are being committed in Tripoli.
Now the people of Eastern Libya are faced with the same treatment.
Mr Speaker, that is the demonstrable need.
Second, regional support.
There must be a clear wish from the people of Libya and the wider region for international action.
It was the people of Libya, through the Transitional National Council, who were the first to call for protection from air attack through a No Fly Zone.
More recently, the Arab League have made the same demand.
Mr Speaker, it really has been remarkable how Arab leaders have come forward and condemned the actions of Gaddafi's government.
In recent days I have spoken with the leaders of Saudi Arabia, Qatar, the United Arab Emirates and Jordan.
And a number of Arab nations have made clear that they are willing to participate themselves in enforcing the Resolution.
This support for this goes far beyond the Arab world.
Last night all three African Members of the UN Security Council voted in favour of the Resolution.
Mr Speaker, the third and essential condition was that there should be a clear legal base.
That is why along with France, Lebanon and the United States we worked hard to draft appropriate language which could command the support of the international community.
Last night the United Nations Security Council agreed that Resolution.
Resolution 1973 "demands the immediate establishment of a ceasefire and a complete end to violence and all attacks against, and abuses of, civilians."
It establishes "a ban on all flights" in the airspace of the Libya in order to help protect civilians"
And authorises Member States to take "all necessary measures to enforce compliance with the ban."
It also "authorises Member States…acting nationally or through regional organisations and or arrangements, and acting in co-operation with the Secretary General, to take all necessary measures…to protect civilians and civilian populated areas under threat of attack…including Benghazi".
Mr Speaker the Resolution both authorises and sets the limits of our action.
Specifically, it excludes an occupation force of any form, on any part of Libyan territory, which was a clear agreement between all the sponsors of the Resolution, including the UK, and of course, also the Arab League.
I absolutely believe this is the right thing both to say and to do.
As our ambassador to the United Nations said, the central purpose of this Resolution is to end the violence, protect civilians, and allow the people of Libya to determine their own future, free from the brutality unleashed by the Gaddafi regime.
The Libyan population wants the same rights and freedoms that people across the Middle East and North Africa are demanding, and that are enshrined in the values of the United Nations Charter.
Resolution 1973 puts the weight of the Security Council squarely behind the Libyan people in defence of those values.
And our aims are entirely encapsulated by that Resolution.
Mr Speaker, demonstrable need, regional support and a clear legal base: the three criteria are now satisfied in full.
Now that the UN Security Council has reached its decision there is a responsibility on its members to respond.
And that is what Britain - with others - will now do.
Mr Speaker, the Attorney General has been consulted and the government is satisfied that there is a clear and unequivocal legal basis for the deployment of UK forces and military assets.
The Security Council has adopted Resolution 1973 as a measure to maintain or restore international peace and security under Chapter VII of the United Nations Charter.
The resolution specifically authorises notifying Member States to use all necessary measures to enforce a No Fly Zone and to protect civilians and civilian populated areas, including Benghazi.
The Cabinet has met this morning.
They have agreed that the UK will play its part.
Our forces will join an international operation to enforce the Resolution if Gaddafi fails to comply with its demand that he ends attacks on civilians.
The Defence Secretary and I have now instructed the Chief of the Defence Staff to work urgently with our allies to put in place the appropriate military measures to enforce the Resolution - including a No Fly Zone.
And I can tell the House that Britain will deploy Tornadoes and Typhoons as well as air-to-air refuelling and surveillance aircraft.
Preparations to deploy these aircraft have already started and in the coming hours they will move to airbases from where they can start to take the necessary action.
The government will table a substantive Motion for debate next week.
But I am sure that the House will accept that the situation requires us to move forward on the basis of the Security Council resolution immediately.
I am sure that all sides of the House call upon Colonel Gaddafi to respond immediately to the will of the international community and cease the violence against his own people.
I spoke to President Obama last night and to President Sarkozy this morning.
There will be a clear statement later today setting out what we now expect from Colonel Gaddafi.
Mr Speaker, any decision to put the men and women of our armed services into harms' way should only ever be taken when it's absolutely necessary.
But we simply can not stand back and let a dictator whose people have rejected him, kill his people indiscriminately.
To do so would send a chilling signal to others striving for democracy across the region.
And neither would it be in Britain's interests.
Let us be clear where our interests lie.
In this country we know what Colonel Gaddafi is capable of.
We should not forget his support for the biggest terrorist atrocity on British soil.
We simply can not have a situation where a failed pariah state festers on Europe's southern border.
This would potentially threaten our security, push people across the Mediterranean and create a more dangerous and uncertain world for Britain and for all our allies as well as for the people of Libya.
That is why today we are backing our words with action.
The choice we have made is to play our part in joint international action to enforce international law:
to uphold the will of the United Nations Security Council
to respond to the calls from Arab countries and the Arab League
and to do the right thing for the people of Libya who want greater freedoms, and above all for the UK's own national interest.
I pay tribute to the brave members of our armed forces who will be carrying out this work.
And I commend this Statement to the House."