A rattled no campaign in the Scottish independence referendum was accused of panic and bogus bribes on Sunday after George Osborne vowed that "a credible timetable and process" will be agreed to develop further devolved powers.

Speaking a day after the first poll showing the yes campaign in the lead emerged, the chancellor said the Conservatives, Labour and the Liberal Democrats would agree to discuss proposals involving "much greater" fiscal autonomy for Scotland.

Offering Scotland more power over tax rates, spending and welfare, the proposals would be ready for implementation in the first Westminster parliamentary session after the 2015 general election, Osborne added.

No campaign sources said the move to set out this process just 11 days before the vote had long been planned, though it emerged the morning after a YouGov poll for the Sunday Times showed a two-point lead for yes, once undecideds are eliminated.

The unexpected poll galvanised Westminster and sent the pound falling on currency markets, with Scotland's future position in the pound still uncertain.

Sterling fell nearly 1% to around $1.6165, reaching lows not seen since November, when trading opened in Asian markets on Monday.

The referendum was likely to have been the dominating topic as David Cameron spent the weekend at Balmoral, though Buckingham Palace reiterated the Queen remained neutral on the subject. She will be in Scotland on the day of the vote but the Palace said that was part of her normal schedule.

The Osborne initiative had a shaky start when the Scottish secretary, Alistair Carmichael, was forced to counter the impression left by the chancellor that the package itself would include greater devolution of powers than already agreed by the parties in a joint statement in June.

Labour, the Lib Dems and the Tories have differing devolution packages, and this week's initiative is designed to remind voters of the commitment to so-called devo max, as well as the process that guarantees it is delivered. "The aim is to make sure the Scottish people believe this package is credible, has a timetable and will be delivered on," said one Scottish government source. First minister Alex Salmond, riding the crest of a potentially historic wave launched by the explosive findings of a single polling company, YouGov – which gave a lead for yes at the weekend – accused Osborne of "a panicky last-minute measure because the yes campaign is winning on the ground". He added: "The evidence for that is overwhelming."

He said: "We're expected to believe that secretly, behind the scenes, after hundreds of thousands of people have already voted, there is a radical new deal on the constitution that is agreed by the Westminster parties. Well, there is a radical new deal on the constitution – it's called independence."

Cameron knows his own future as prime minister may lie in the hands of Scottish voters. Although he has insisted his own career is not on the ballot paper, he knows he will be blamed by some of his own party for pressing ahead with the high-risk referendum.

For Labour, the prospect of the permanent loss of as many as 40 Labour MPs representing Scottish seats would be "a disaster", the former Labour cabinet minister David Blunkett openly admitted on Sunday.

Labour politicians fear the vote for separation is in part driven by a disillusionment with politics among core Labour voters, as a well as pessimism about Labour's chances of being elected in 2015. These are emotional instincts that are difficult to combat and not susceptible to rational argument or even threats about the consequence of separation for the Scottish economy, the staple diet of the no Campaign so far.

Rupert Murdoch, chairman of News Corp, publisher of the Sunday Times and the Sun and a growing advocate of devolution, claimed on Twitter that Salmond's private polls showed 54%-46% support for yes and predicted a desperate last 10 days as the establishment fought to save the union. He said the problem for Scottish parties now offering much new autonomy was the lateness of the promise and its credibility.

In the bid to regain the initiative, and shift away from the negative tactics of recent weeks, Osborne, speaking on BBC's Andrew Marr Show, said: "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."

Gordon Brown claimed Labour had for some weeks been pressing for a more definitive statement about the timetable for the delivery of extra powers. "I think when people see the full scale of the powers the Scottish parliament will have, and our ability to do things while retaining the benefits of the UK, including the currency, I think they are going to decide on the extended powers of the Scottish parliament within the UK."

Brown added: "I hope the other parties will support what is a Labour proposal, a Labour initiative, so that these powers are guaranteed, and so a No vote doesn't mean nothing happens, a No vote means we move quickly to the delivery of extra powers."

He is due to launch a six-day, 30-destinations tour of Scotland's heartlands aimed at convincing undecided voters of the case for a patriotic no vote.

The shadow foreign secretary Douglas Alexander has long been arguing for a Scottish Convention, or broader consultation, including the Scottish Nationalists to work out the details of so-called devo max.

But the Unite general secretary Len McCluskey complained "Right at the outset we argued that there should be two questions on the ballot paper: independence should be one and the other should be devo max. I have to say we were dismissed out of hand, but had there been two questions there would be none of the concerns that are being expressed now. He said while the yes campaign was campaigning on a vision of change, the no campaign appeared to be backing the the status quo.

"The truth is that the people of Scotland are not happy with the status quo", he said

. The three unionist parties have different devolution packages. Labour has proposed members of the Scottish parliament be empowered to increase – but not cut – the 40p and 45p income tax rates without touching the basic rate, so preventing the Scottish Nationalists undermining the union through tax competition. Labour has also said it would replace council tax with a new system that would see Scots in the largest properties pay more.

Control over the £1.7bn housing benefit budget would be devolved. The Lib Dems' Campbell II report and the Scottish Conservatives' Strathclyde commission would give the Scottish government full control over both the rates and bands of income tax.The Liberal Democrats would also devolve air passenger duty, capital gains tax and inheritance tax, as part of a wider federal settlement: under Labour these taxes would remain reserved, while the Conservatives propose devolving the former but not the latter two taxes.

If Scots vote yes …

• Alex Salmond will confirm his "Team Scotland" of negotiators – expected to include his deputy, Nicola Sturgeon, along with senior cross-party figures – within a week or so. David Cameron, if he has ridden out calls for his resignation, will set up a similar negotiating team for the remainder of the UK.

• To minimise market instability and avoid a run on the pound, Cameron must confirm quickly the UK's stance on the status of sterling and the splitting of debt with Scotland. Other subjects for immediate discussion would include dividing up oil and gas reserves.

• All 28 EU states are expected to meet by the end of 2014 to give the European commission a mandate to investigate Scotland's EU membership. Salmond must also begin talks with Nato. Both situations are without precedent and the negotiations are likely to be complex and protracted.

• Before the general election campaign begins in earnest, the UK parties will have to decide what role Scotland's 59 MPs at Westminster will have after May 2015. They will technically remain in the Commons, but only until independence day.

• Salmond has set midnight on 23 March as the target date to declare Scotland an independent country. Holyrood will then be dissolved for the first elections to an independent parliament.