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.