Union leaders have launched a highly critical attack on the anti-independence parties accusing them of dragging their feet before their 11th-hour appeal to voters to back No.

The general secretary of the STUC Grahame Smith said that the timing and handling of an announcement on extra powers for Scotland risked making the move appear insincere and meaningless.

Fronted initially by the Chancellor George Osborne it also looked like a last minute "political fix constructed in Westminster", he said.

The plan was first outlined by Mr Osborne on the BBC's Andrew Marr Programme on Sunday, just hours after an opinion poll giving the Yes camp the lead on 51 per cent triggered shockwaves north and south of the border.

Mr Smith said: "The way the message was delivered it gave the impression that this was a political fix, constructed in Westminster without really consulting the people of Scotland and organisations and institutions like ourselves who have long been involved in this debate.

"Even if the intention is well-meaning it is certainly not going to be seen as sincere and meaningful and therefore could be counter productive.

"We called on the Better Together parties to come together (and make an announcement on extra powers) in February this year.

"They have had lots of time to do something and yet they are doing this now, within days of the referendum and when tens of thousands of people have already voted."

He added that the TUC had not been consulted about the process of greater devolution to Scotland, beyond an initial question months ago if it would be willing to take part if a body such as a constitutional convention was created.

Last night Labour leader Ed Miliband appeared to divide the trade union movement heaping praise on those which backed a No at a dinner with union leaders, many of whose organisations, including the TUC, the STUC and the UK's largest trade union, Unite, remained neutral.

He said: "By working together for a Labour government across the UK, we can freeze energy bills, raise the minimum wage, introduce fairer taxes, and put our young people back to work.

"Compare this with what the SNP is offering. As well as huge unanswered questions from currency to jobs, they propose cuts in corporation tax, no energy price freeze, no commitment to the 50p tax rate and the end to the social justice in the UK.

"Saying "No Thanks" to separation is also about saying yes to more devolution.

"With more decisions being made in Scotland, by Scots.

"With a stronger Scottish Parliament. With more powers guaranteed.

"I say we should get the process of further devolution under way right after the referendum."

He told the entire group: "You know that we achieve more together than we can do alone."

The message went down badly with some.

One union source said last night: "Because we have respected the views of our members (and remained neutral) does not mean that we are bad trade unionists, or that we care any less about workers".

However, the beginnings emerged of a potential blame game over the referendum within the union movement also emerged.

One trade union source said that it "would have been helpful" if more unions had come out to back a No vote.

Last week the RMT rail workers union in Scotland came out for a Yes vote.