Scotland's First Minister has claimed the campaign for the union is in "disarray" after the leaders of the three main Westminster parties announced a last-minute trip north to bolster support for a No vote in next week's independence referendum.

Prime Minister David Cameron and Labour leader Ed Miliband have cancelled their weekly Prime Minister's Questions clash and will travel north with Deputy Prime Minister Nick Clegg.

The three men will each make separate visits to Scotland as they explained they wanted to be out "listening and talking to voters" about the choice they face on September 18.

Alex Salmond said: " The message of this extraordinary, last-minute reaction is that the Westminster elite are in a state of absolute panic as the ground in Scotland shifts under their feet."

The SNP leader added: "The No campaign is in complete and utter disarray, and they are making this farce up as they go along.

" Together, David Cameron, Ed Miliband and Nick Clegg are the most distrusted Westminster politicians ever - and their collective presence in Scotland will be another massive boost for the Yes campaign.

"The No campaign think that they are losing this campaign - and these hugely distrusted Westminster leaders trooping up to Scotland is only going to boost that process.

" The No campaign are making blunder after blunder, but this is by far the biggest yet."

Polls show that that campaign for Scotland's future is increasingly too close too call, with one survey today putting the Yes and No campaigns neck and neck among those who are certain to vote while another poll at the weekend had support for independence in front for the first time.

In the wake of that, the three Westminster leaders issued a joint statement in which they declared: ''There is a lot that divides us - but there's one thing on which we agree passionately: the United Kingdom is better together.

''That's why all of us are agreed the right place for us to be tomorrow is in Scotland, not at Prime Minister's Questions in Westminster."

Mr Cameron said: "One thing I'm sure we will all say is that it's a matter for people in Scotland to decide, but we want you to stay.''

Mr Miliband said: "I want the Scottish people to be in no doubt that the view, I believe from the whole of the UK, is that, yes, things need to change, but let's change this together by voting No in the referendum.

"Please stay with us so we can change Britain, we can change Scotland together."

They spoke out after the leaders of Conservatives, Labour and Liberal Democrats at Holyrood joined forces to get behind a new, more rapid timetable, for further devolution in the event of a No vote.

Mr Salmond, who was campaigning in the centre of Edinburgh, claimed, however, that his unionist opponents were "making up the reconfiguration of the United Kingdom on the back of an envelope".

He insisted: " What we've found in the last 48 hours, as far as anyone can tell, is there doesn't seem to be anything new in terms of powers on offer, beyond what was on offer in the spring, which was largely dismissed by the majority of people in Scotland.

"Quite rightly so, because if you take Labour's proposal, for example, it would only put one-fifth of the revenue base of Scotland into the hands of the Scottish Parliament.

"That wouldn't allow us the job-creating powers that are so desperately needed, the powers to protect our public services and to embrace the more prosperous and fairer society, which is the central message of the Yes campaign."

He added: " Repackaging, after 48 hours of total confusion, exactly the same packages that were on offer in the spring.

"All that tells us is the No campaign is both in fundamental disarray and terminal decline."

A Buckingham Palace spokesman stressed the Queen believed the decision over whether or not Scotland remains in the UK was for voters north of the border to judge.

The Prime Minister made a private visit to the Queen at Balmoral, her highland retreat in Aberdeenshire at the weekend, but the apparent momentum behind the Yes campaign has led to reported calls for her to publicly declare her views.

A Buckingham Palace spokesman said: "The sovereign's constitutional impartiality is an established principle of our democracy and one which the Queen has demonstrated throughout her reign.

"As such the monarch is above politics and those in political office have a duty to ensure this remains the case.

"Any suggestion that the Queen would wish to influence the outcome of the current referendum campaign is categorically wrong. Her Majesty is simply of the view this is a matter for the people of Scotland."

Mr Clegg said: "I think it's important that everyone who is voting in this referendum knows that people like me, who don't have a vote in the referendum, desperately hope that they will choose that Scotland should remain a part of this very successful family of nations, because I think we are all stronger and better off and more prosperous and more secure in an uncertain world when we do things together, rather than turn our backs on each other.

"Of course, we have huge differences between our countries and will have more in the future between Scotland and other parts of the United Kingdom, but we can have those differences and still work together as a family of nations."

Labour Former deputy prime minister Lord Prescott urged voters not to end the union because they do not like the Conservatives.

In an article for the Daily Mirror, he wrote: " Now I know it's galling to see a bunch of jumped up clueless English public school boys running the UK Government when you didn't vote for them. I spent 18 years in opposition fighting the Tories in the Commons

"But leaving a union that has delivered huge cultural, social and economic benefits for millions of people for centuries because you don't like Cameron and Osborne is like walking away from a fight with Lord Snooty and his Posh Pals.

"That's why I'm up here fighting for Gordon's Labour plan and devolved English regions. To do that, we need Scotland's support within a United Kingdom."

He added: " We've got the Bullingdon Boys on the run down south but we need your help to finish the job. If you leave, we'll have to stand alone.

"So stick with us in this fight and we'll both kick them in the ballots at the General Election. United we stand. Divided we both fail.

"Please don't walk away from the fight. Britain needs you now more than ever."