David Cameron, Nick Clegg and Ed Miliband are making the biggest "blunder" yet of the pro-UK campaign by making a last minute trip to Scotland ahead of next week's independence referendum, the country's First Minister said.

Alex Salmond hit out after it was announced the Prime Minister and Labour leader are to miss Prime Minister's Questions tomorrow to come to Scotland in a bid to drum up support for the union.

The Scottish First Minister claimed: "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."

In a joint statement the Tory leader, the Labour leader and the Liberal Democrat leader said they wanted to be out "listening and talking to voters" about the choice they face on September 18.

It comes after the leaders of the three main pro-union parties in Scotland joined forces to pledge more powers for Scotland if voters reject independence.

Mr Cameron said: "Let's be frank, there's a lot that the political leaders disagree about but there's one thing that we all agree about passionately and that is that our United Kingdom is better off if we stay together.

"So tomorrow the right place to be isn't Westminster at Prime Minister's Questions, it is being in Scotland, listening to people, talking to people."

As the three Westminster leaders declared their plans, the saltire was hoisted over Number 10 Downing Street.

But that was not without problems, with the Scottish flag initially making it part of the way up the flagpole before falling down.

Afterwards Mr Salmond hit out: "The No campaign is in complete and utter disarray, and they are making this farce up as they go along."

A Panelbase poll for the pro-independence campaign group Yes Scotland earlier this month found that fewer than a fifth of Scots (19%) trust Mr Cameron to stand up for Scotland's interests, with just 17% believing Mr Miliband would do this and 12% trusting Mr Clegg to do so.

Mr Salmond said: "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 SNP leader added: "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.

"It is also a commentary on the farcical event of their three Scottish representatives today, who had barely finished their press conference when it was obviously judged to be completely ineffective.

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

Mr Miliband said: "This is about the future of our country.

"That is why it is right that tomorrow I am not at Prime Minister's questions shouting across the despatch box, but I am in Scotland talking to the people of Scotland, listening to them.

"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."

He insisted there was a "very, very large measure of agreement" between the parties over the key elements of the package of extra devolution to be offered in the case of a No vote.

"Over greater powers of taxation so that you can have a more progressive tax system if that is what is decided in the Scottish Parliament," he added.

"Over issues like housing benefit so that homes can be built and you can deal with the housing benefit issue. About getting people back to work, about apprenticeships, building on the powers that already exist.

"So there is a very, very large measure of agreement and there is no doubt, there is no uncertainty, that greater devolution will happen in the event of a No vote."

Asked if a failure to prevent Scotland breaking away from the union would make his and David Cameron's leaderships untenable, he replied: "That doesn't arise. And in any case this is much bigger than any one individual."

Mr Salmond, who was campaigning in the centre of Edinburgh, said the Westminster parties were "in total disarray" and were "making up the reconfiguration of the United Kingdom on the back of an envelope".

Former prime minister Gordon Brown set out a timetable for further devolution, saying a ''command paper'' should be published by the present UK Government setting out all the proposals for change no later than the end of next month.

A white paper would be drawn up in November after a period of consultation, with draft clauses for legislation expected in January.

But Mr Salmond 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."

The First Minister went on to state that if Scots voted to leave the UK, Mr Cameron should consider his position

"If it comes to a situation where Scotland votes for independence, and he wasn't even prepared to put himself up for democratic debate, then surely, surely his position as Prime Minister would be completely and utterly untenable," the SNP leader said

"We are taking nothing for granted, we've got lots of work to do, we've got many friends helping us along the way, but I think the momentum is with us.

"If we keep doing what we're doing, if we keep it positive, I think we will see a saltire hoisted around Scotland a week on Thursday."

He spoke as MPs on the Political and Constitutional Reform select committee hit out the "vague" promises of more devolution.

The Deputy Prime Minister said that in a political campaign "you don't spend all your time assuming that you are going to be defeated".

He added: "You campaign for what you believe in. We're not working on contingency plans because we are fighting with every means that we can for what we believe in, which is the continuation of a very successful family of nations."

Conservative MP Chris Chope said: "Well, lets hope that in spite of the shambolic way it is being run by the Government, we actually succeed in keeping the UK together.

"In the second televised debate, Alistair Darling was asked what extra powers would come to Scotland in the event of a No vote and he was unable to answer that question.

"And many people say that his failure to answer that question is one of the reasons why the Yes campaign have this new momentum."

Mr Clegg said the parties' proposals have all been in the public domain for months, but said they have now agreed a timetable for implementation.

But SDLP MP Mark Durkan compared the parties to a mobile phone salesman trying to beef up offers to prevent a customer going to the opposition, adding in that this means reform becomes "a penalty shootout where nobody scores".

Mr Chope later told the BBC: "I think there's a lot of scepticism about that sort of promise coming, particularly when it is late in the day and can be attacked as being a panic measure.

"Back in 2012 the Government decided that they wouldn't give the Scots the option of greater devolution, that it was going to be independence or stay as you are.

"The rationale for that was articulated by the Prime Minister saying we didn't want to give a reward for people going for an independence referendum.

"Now, three years later, after a number of people have already cast their ballots in postal votes, we find that Gordon Brown goes off and makes a statement that must be with the authority of the Government because it talks about a white paper and legislative timetable but that hasn't been discussed in Parliament at all."

He added that if Scotland voted Yes it could "create the largest constitutional crisis in our lifetime", and added: "Obviously, the Prime Minister will have lot of questions to answer, not just from backbenchers but from our constituents."

Asked whether the Prime Minister would like people in the rest of the UK to demonstrate their support for the union by flying the saltire or phoning Scottish friends and relatives to urge them to vote Yes, Mr Cameron's official spokesman said that this was a matter for individuals to decide for themselves.

But he added: "The Prime Minister has spoken about this. Certainly, for those who feel strongly like he does - and I think he takes the view that this is the case for a good many people up and down the country - there is an opportunity for people to make their voices heard in terms of sending that message to the people of Scotland that we want you to stay.

"I dare say there are a whole range of ways in which they may choose to do that, but that is for them.

"His message is if you feel strongly, do go out and express your desire and keenness for Scotland to stay in the United Kingdom."

The spokesman revealed that his own partner - a Glaswegian who does not have a referendum vote because she lives outside Scotland - has been calling her family to discuss the independence debate.

Asked why the three party leaders would not be appearing on the same platform during their visits to Scotland, the PM's spokesman said: "It is an opportunity to meet a good number of Scots in a range of places, rather than just one."