Plans to devolve more powers to Scotland inside the UK will be unveiled within days after a shock poll put the Yes camp in the lead for the first time.

Chancellor George Osborne said the final touches were being put to proposals for "much greater" fiscal autonomy and tax-raising abilities.

He insisted the YouGov research for the Sunday Times - which found pro-independence campaign ahead by 51% to 49% - should galvanise those who wanted to keep the union together.

Speaking on the BBC's Andrew Marr show, Mr Osborne denied that dire warnings about the dangers of splitting up had backfired.

He said: "This country faces a very, very big choice. Scotland faces a very big choice.

"If people were in any doubt that they can stay at home, that they don't need to go out to the polls and vote No to avoid separation, they won't be in that doubt today.

"They should also be in no doubt about the consequences of this decision - one of which is that Scotland will not be sharing the pound as an independent country with the rest of the UK if the separatists win the vote."

Mr Osborne said sharing the currency after independence would be equivalent to a couple divorcing but retaining the same bank account.

"No ifs, no buts. We will not share the pound if Scotland separates from the rest of the UK," he said.

The Chancellor said it was "clear" Scotland wanted more autonomy and the Tories, Labour and the Liberal Democrats had agreed to "deliver" on that.

He added: "You will see in the next few days a plan of action to give more powers to Scotland. More tax powers, more spending powers, more plans for powers over the welfare state.

"That will be put into effect - the timetable for delivering that will be put into effect the moment there is a No vote in the referendum.

"The clock will be ticking for delivering those powers, and then Scotland will have the best of both worlds.

"They will both avoid the risks of separation but have more control over their own destiny, which is where I think many Scots want to be."

The reforms would include "much greater" fiscal autonomy and control over tax rates as well as more powers over welfare rates.

Mr Osborne also played down speculation that Prime Minister David Cameron could be forced to resign in the event of a Yes vote.

"This is not about the future of the British Government in Westminster. This is not about the future of myself or David Cameron or anyone else," he said.

But Scottish Deputy First Minister, Nicola Sturgeon, says people in Scotland will not be fooled by an offer of more powers for Holyrood from a unionist campaign which is "engulfed in panic"

She said: "I think what we will see is the No campaign engulfed in panic.

"I think the No campaign is missing the fact that this campaign in Scotland has moved beyond any place where people can have the wool pulled over their eyes.

"One of the really invigorating things about this campaign, and for politicians one of the challenging things, is that we have now got a well-informed population that is capable of seeing through what the politicians say and coming to their own decision.

"That's why we see the Yes campaign ahead and why I'm confident, although it will take really hard work, we will see Yes win on September 18."

She claimed that it "increasingly looks as if the No campaign think people in Scotland are daft", adding: "If the No campaign parties had any serious intention of delivering substantial new powers for Scotland, then why has it taken until 10 days before polling day, with a poll showing Yes in the lead, for them to come up with this?

"There is no option of more powers short of independence on the ballot paper, there is no guarantee whatsoever that if Scotland votes No we will get a single additional power for the Scottish Parliament.

"If people want the powers we need to protect our public services, protect the health service, ensure that we can create jobs, grow our economy, protect the vulnerable through a decent social security system, the only way to get that is to vote for the powers a Yes vote will deliver.

"That's the only option that puts control into our hands, to vote No leaves these future decisions in the hands of the Westminster establishment and I don't think that after this wonderful, invigorating debate that we've had in Scotland, that that is what people want to do

"I think the debate in Scotland has gone beyond the point where people can be fooled and taken in by empty promises from Westminster parties."