Scotland's First Minister Alex Salmond and U.K. Prime Minister David Cameron respond to Scotland's decision to stay in the U.K. (Updated 3:45am ET, Sept. 19)

LONDON—Prime Minister David Cameron on Friday pledged to honor his commitment to give more powers to Scotland after voters chose to stay in the U.K., but in a surprise move, the British leader also endorsed greater autonomy for England, Wales and Northern Ireland.

Scottish voters awoke Friday to find their country will still be part of the United Kingdom after a historic referendum. WSJ's Jenny Gross reports from Edinburgh. Photo: AP

Mr. Cameron's proposal suggests that the pledges he and other pro-union parties made to grant Scotland powers over tax, spending, and welfare could trigger major changes in the way the whole country is governed.

"Just as the people of Scotland will have more power over their affairs, so it follows that the people of England, Wales and Northern Ireland must have a bigger say over theirs," he said outside his official residence, 10 Downing Street.

"The rights of these voters need to be respected, preserved, and enhanced," he said.

Supporters from the "no" campaign celebrate in Edinburgh. Reuters

Mr. Cameron gave no details, but such a move would be a substantial change for the U.K., where most power has been centralized in London.

Northern Ireland and Wales already have regional parliaments with some autonomy, including over health and education, giving England more to gain from such a proposal.

There has been a long-running debate about whether lawmakers in London representing constituencies outside England should have a say on some affairs that only affect England, while those in England have no say on similar matters that affect Scotland, Wales, and Northern Ireland.

Former Foreign Secretary William Hague had been tasked with drawing up plans and a cabinet committee was to be set up immediately, Mr. Cameron said, adding that he hoped other political parties would contribute.

Ed Miliband, the leader of the opposition Labour Party, also welcomed the Scottish vote and said he supported further devolution.

"We will deliver on stronger powers for a stronger Scottish parliament," he said at an event in Glasgow. "And we will also meet the desire for change across England, across Wales, across the whole of the United Kingdom."

Mr. Cameron, Mr. Miliband and the Liberal Democrats' Nick Clegg promised Scotland the new powers as recent polls showed Scots might vote in favor of independence and end the 307-year union.

On Friday, the prime minister said work would begin to grant the devolved government more control, with plans agreed upon by November and draft legislation published by January. He called for the rest of the country to get the same powers at the same time.

"So just as Scotland will vote separately in the Scottish parliament on their issues of tax, spending, and welfare, so too, England, as well as Wales and Northern Ireland, should be able to vote on these issues," he said.

Just as the people of Scotland will have more power over their affairs, so it follows that the people of England, Wales and Northern Ireland must have a bigger say over theirs.

—Prime Minister David Cameron

The prime minister said he was delighted that Scots had rejected independence in the referendum, in which 55% of votes choose to stay with the U.K.

Earlier, Alex Salmond, the leader of the Scottish National Party, accepted the result of the vote but urged pro-union parties to devolve powers quickly.

There are still major hurdles to devolution in Scotland. Chief among these is that the three major parties don't yet agree on which powers to devolve. They have published competing visions for Scottish "home rule" over the past year. The differences could add as much as billions of pounds a year in revenue and substantially more autonomy.

Discussions are to begin immediately over which powers should be devolved. The Westminster political leaders have outlined a four-stage process, starting with cross-party talks on which further powers to devolve.

In October, the parties will publish a parliamentary document setting out a range of possible tools and responsibilities that could be devolved. A public consultation on the proposals will follow ahead of the publication of preliminary legislation in November, and a formal bill will be put before parliament in January.

Mr. Cameron said it was right that the Scotland referendum had presented voters with a binary choice of whether to stay or go.

"Because now the debate has been settled for a generation, or as Alex Salmond has said, perhaps for a lifetime. So there can be no disputes, no reruns. We have heard the settled will of the Scottish people," Mr. Cameron said.

—Jenny Gross and Jason Douglas contributed to this article.

Write to Nicholas Winning at nick.winning@wsj.com