DAVID Cameron's government has insisted the pro-Union parties will still win the independence referendum as they prepare to unveil a last-ditch attempt to woo undecided voters with a new "action plan" for Scotland.

Labour, the Liberal Democrats and the Conservatives will unveil a joint timetable towards greater autonomy on Wednesday after a poll putting Yes ahead for the first time sent shockwaves through the political establishment.

But the announcement is not expected to guarantee Scotland any specific new powers and the move comes too late for tens of thousands of people already thought to have voted by post.

Last night a Downing Street source said: "We will still win this," despite the poll that showed Yes ahead by 51 per cent to 49 per cent. The headline figures exclude those who would not vote or are undecided. With those groups included, 47 per cent backed independence and 45 per cent wanted to stay.

It triggered renewed claims that Mr Cameron would have to resign if Scots plump for independence.

In another move to stem the move to Yes, the LibDems will put former leader Charles Kennedy at the forefront of their campaign for the next 10 days.

A party source said: "Undecided voters trust him."

Labour is also stepping up its campaign, with former Prime Minister Gordon Brown to appear at a rally in Loanhead near Edinburgh. Shadow chancellor Ed Balls will also be north of the Border.

Independence campaigners said the moves were a sign of panic. Canon Kenyon Wright, seen by many as the architect of Scottish devolution, said this week's cross-party announcement had a "whiff of desperation about it, especially considering that 100,000 Scots may have already voted".

He added: "This looks like another bribe in a last-ditch attempt to encourage Scots to vote against the full range of powers offered by a Yes vote."

Last night a series of messages by Rupert Murdoch on Twitter intensified rumours that one of his papers, such as The Scottish Sun, could come out for independence.

Labour also sought to quell a growing row, denying claims Labour leader Ed Miliband had suggested the party had plans for guards on the Border in the event of a Yes vote.

Pro-Union sources said Wednesday's announcement would be "the meat on the bone" of the process for more powers after a No vote. They will include powers on tax, welfare and public spending.

The cross-party announcement will come just days after Mr Brown appeared to blame the Tories for the close polls. He said it was difficult to persuade Scots after the Tory-led welfare cuts and tax cuts for the rich.

Yesterday Chancellor George Osborne said an "action plan" would set "the clock ticking" on the push for more powers and issued a strong warning against the dangers of voting Yes, saying: "No ifs, no buts, we will not share the pound,"

But his appearance on the BBC's Andrew Marr Show raised hopes the pro-Union parties would set out an agreed set of devolved powers for Scotland. Scottish Secretary Alistair Carmichael and Better Together leader Alistair Darling later toured broadcasters to dampen those expectations.

Mr Brown, campaigning in Kirkcaldy, claimed the move to press a timetable was "a Labour initiative, so that these powers are guaranteed, and so ... a No vote means we move quickly to the delivery of extra powers".

But Alex Salmond said: "Are we expected to believe, after hundreds of thousands have already voted, that there's a radical new deal?"