David Cameron sets out UK-wide changes 'to build better future'
David Cameron has said it is time for the UK "to move forward" after Scotland voted against independence.
The PM said he was "delighted" by the result, which gave the UK a chance to change "for the better".
He said there had to be a "fair and balanced" settlement with English MPs deciding on laws applying to England.
But defeated SNP leader Alex Salmond warned against any delay in shifting powers to Scotland as he announced his decision to step down.
"For me as leader, my time is nearly done," he said. "For Scotland, the campaign continues and the dream shall never die."
Scotland's First Minister explained his decision to quit just hours after Scotland voted decisively to stay in the United Kingdom by 2,001,926 votes to 1,617,989 - about 55% to 45%.
The vote is the culmination of a two-year campaign. Talks will now begin on devolving more powers to Scotland.
The people have spoken. But it's not over.
BBC political editor Nick Robinson
The people have spoken. Scotland has rejected independence. The result has been accepted by both sides. So that you might think is that. Not a bit of it.
The fact that over 1.5m British citizens voted not to remain part of the UK, the fact that a majority in Scotland's biggest city - Glasgow - backed independence, the fact that the Westminster establishment briefly thought this vote was lost, is the reason for that.
The leaders of the three UK parties are now promising significant constitutional change and not just for Scotland but for England, Wales and Northern Ireland as well.
They have agreed on a timetable for giving more powers to the Scottish Parliament but are a long, long way from agreeing proposals.
Mr Salmond said he was "immensely proud" of his Yes campaign and serving as Scotland's First Minister had been "the privilege of my life", but he conceded that the SNP would benefit from new leadership to take the process on.
The party had "the opportunity to hold Westminster's feet to the fire on the 'vow' that they have made to devolve further meaningful power to Scotland," he said. "This places Scotland in a very strong position."
But while he would continue to serve as MSP for Aberdeenshire East, he had decided to stand down after the party's annual conference in November.
"We lost the referendum vote but can still carry the political initiative," he said. "More importantly Scotland can still emerge as the real winner."
In a statement outside Downing Street Mr Cameron defended the decision to hold the referendum, saying it was right that the SNP's majority in Holyrood was respected.
He said Lord Smith of Kelvin had agreed to oversee the process of devolving more powers over tax, spending and welfare to Scotland, with draft legislation by the end of January.
Mr Cameron added that the rights of other people in the UK needed to be "respected and enhanced". He said he had long believed that a crucial missing part was England. He said "the millions of voices of England must be heard".
The Leader of the Commons William Hague has been asked to draw up plans for what would be a fundamental change at Westminster - that only English MPs could vote on English matters.
The politics of the English question
BBC deputy political editor James Landale
The Downing Street constitutional declaration - as it will become known - marks the start of what potentially could be massive constitutional change.
In particular, the prime minister has promised to give English MPs a greater say over legislation that affects England. He made clear this would cover the same issues over which Scotland will have greater control - tax, spending and welfare. And the changes will be agreed at the same pace with draft legislation by January.
But David Cameron did not spell out the detail, leaving a policy vacuum that will now be filled by Conservative MPs and an army of constitutional experts and think tanks. Everything from a full English parliament to complicated plans for English grand committees will be discussed.
The risk for the PM is that he loses control of this debate.
Mr Hague insisted there was a "very clear commitment" to the Scottish reforms pledged by the three main UK parties, but he argued that the English question had to be resolved at the same pace.
"I think it would be inconceivable to go ahead with a further important stage and measure of devolution to parts of the United Kingdom, without addressing this issue," he told the BBC.
"Of course it's been an anomaly for quite a long time now that Scottish MPs can vote on everything happening in England, but we the English MPs can no longer do so in Scotland, and indeed nor can the Scottish.
"But it will become absolutely acute - it will become absolutely indefensible with further devolution - and I think people need to know at the time of the general election next May where we all stand on that, whether we've tried to reach an agreement, and if not, it's something they can decide on in the general election."
BBC political correspondent Iain Watson said the proposal to restrict voting rights for Scottish MPs could undermine a future Labour government - theoretically there could be a Labour PM who lacks a majority of English MPs so is unable to get health or education issues through parliament.
But Labour leader Ed Miliband, arriving at his party's conference in Manchester, said he would not allow the moment "to be used for narrow party political advantage".
Instead he announced plans for a full constitutional convention "rooted in our nations and regions... to ensure decisions are taken closer to the families and businesses".
"These issues can no longer be fixed solely by politicians or prime ministers trying to shore up their position in their own party," he said. "The people need to be given a voice too."
He did not comment on proposals for English-only votes in Parliament, instead calling for more powers to be devolved to regions within England.
Deputy Prime Minister Nick Clegg said it was time for the "clammy grip" of Westminster and Whitehall to be released "so that communities, families, cities, towns and villages across the UK feel that they have more say over their destiny than is currently the case".
Mayor of London Boris Johnson said the result was "a great day for Britain" and pressed the case for English devolution. "What is sauce for the goose has got to be sauce for the gander," he added.
Meanwhile, Conservative MP Owen Paterson, who was sacked by Mr Cameron as environment secretary in July, demanded an immediate recall of Parliament to debate a new constitutional settlement.
He said it had been "completely unacceptable that right at the end of the campaign we have an ex-Labour leader (Gordon Brown) galloping off up to Scotland making some very rash promises of extensive new powers to the Scottish people - apparently with the endorsement of all three UK party leaders."
Conservative Bernard Jenkin said he supported English votes for English laws, but claimed Mr Cameron's "No" campaign had been "patronising, over bearing," and had given very little clarity about the implications of independence - "just rather a lot of scare stories".
Ex-Labour minister Frank Field urged the Labour leadership to come up with its own answer to the "English question" as soon as possible, warning that the party could not afford to drag its heels or be seen as "anti-English".
UKIP leader Nigel Farage said it was now time for a "constitutional convention to find out how a fair UK would work".
"I think England needs a voice," he said. "We've heard a lot from Scotland. The tail can't continue wagging the dog any longer. We must have English MPs voting on English only matters."
Graham Brady, chairman of the Conservative MPs' 1922 Committee, said he could envisage parliament having English-only days - when English MPs vote on English matters.
Speaking to the BBC's Newsnight programme, he said a separate English parliament could be costly and bureaucratic, but one parliament could sit on different days of the week for different matters.