LONDON (AP) — England and Scotland work "so much better together" than apart, British Prime Minister David Cameron said Thursday, as he appealed to Scots not to break up the United Kingdom by voting for independence.

In a speech in Edinburgh before talks on the ground rules for a referendum, Cameron said Britain was "a warm and stable home that billions elsewhere envy" — and dangled the prospect of more autonomy for Scotland if it chose not to leave.

"I believe in the United Kingdom," Cameron said. "I'm a unionist — head, heart and soul.

"Of course Scotland could govern itself. So could England. But we do it so much better together."

Cameron was in the Scottish capital for his first meeting on the issue with Scottish leader Alex Salmond, whose separatist party has long campaigned for Scotland to leave its neighbors behind for the first time in more than 300 years.

Salmond is seeking to hold an independence referendum in September 2014, hoping that a separation from London would be completed with a May 2016 election for the Scottish Parliament.

However, with opinion polls showing that only about a third of Scots favor splitting the nation, Cameron and other opponents are pressing for the vote to be held earlier.

They also want a straight "yes or no" question rather than a third option, suggested by Salmond, of increased autonomy short of outright independence.

After the meeting, Salmond said talks "have moved on quite substantially," with the only remaining disagreement being how many questions would be on the ballot.

But Cameron said that "on the issue of independence, separating Scotland, leaving the United Kingdom, I am afraid there wasn't much progress."

"I believe that we need to put a straightforward and simple and legal question to the Scottish people in good time, Cameron said.

And he said Scotland could get more powers if it said no to independence.

"If the answer to the question is that Scotland wants to stay in the United Kingdom, then further options for devolution are on the table," he told the BBC.

Scotland and England united in 1707 to form Great Britain, but Scotland gained significant autonomy after voting in 1997 to set up the Edinburgh-based Scottish Parliament, which has power over education, health and justice and can make minor alterations to income tax. London retains primacy on all matters relating to Britain as a whole — including defense, energy and foreign relations.

Cameron's government and Salmond have differed on the date of the referendum, what will be on the ballot paper and whether 16- and 17-year-olds should be allowed to vote.

In his Edinburgh speech, Cameron hinted that independence could damage Britain's status in Europe, within NATO and put at risk the U.K.'s permanent seat on the U.N. Security Council. He said Scotland would be safer and richer if it remained a part of the U.K., along with England, Wales and Northern Ireland. Wales and Northern Ireland also have devolved administrations with limited powers.

But his overall tone was emollient. Cameron stressed that Scotland had the right to choose its own destiny, but said he hoped it would remain within Britain.

He said that in an era of globalization and "increasing economic competition from the new, economic powerhouses of the world," there was strength in numbers.

"Nothing encapsulates the principle of pooling risk, sharing resources and standing together with your neighbor better than the United Kingdom," he said.

He also suggested Scotland could be granted more powers within the U.K. if it rejected independence.

He said once the independence question was settled it would be time to ask: "Are there other powers that can be devolved? How can we make the United Kingdom work better?"

Salmond insists that independence would bring greater prosperity, allowing Scotland to better exploit its oil, gas and other energy resources.

And he was skeptical of Cameron's suggestion that rejecting independence would bring more powers for Scotland.

"If the prime minister has an offer to make to the people of Scotland then he should make it now," Salmond said. "He should spell it out now so we can have a clear debate and a clear decision on the alternative futures for Scotland.

"This idea of saying 'well, vote no and we'll give you something later' I don't think is going to convince anyone in Scotland."

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David Stringer contributed to this report.