Scotland’s First Minister yesterday accused the Westminster parties of reneging on their referendum promise to provide new powers to Scotland as Labour and Tory leaders fought over their plans for constitutional change.

Alex Salmond, who announced his resignation after the No vote on Thursday, also claimed that Scottish independence “is now inevitable.”

Mr Salmond said: “When you have a situation where the majority of a country up to the age of 55 is already voting for independence then I think the writing’s on the wall for Westminster.

“The destination is pretty certain — we’re only now debating the timescale and the method.”

His comments came as Prime Minister David Cameron and Labour leader Ed Miliband traded blows with each other on the constitutional crisis which has unfolded following the referendum.

Mr Cameron insisted the timetable for further devolution was “brisk but achievable” and that “new powers over tax, spending and welfare are on their way to Scotland.”

He promised a white paper by November and draft legislation by January.

Mr Miliband, speaking from the Labour Party conference in Manchester, slammed Mr Cameron for linking the Scottish devolution timetable to a proposal for “English votes on English laws.”

He said: “David Cameron made a promise, he didn’t make a conditional promise, and he’s going to be kept to that.

“We’ve spent two years trying to keep our country together. Let’s have a proper constitutional convention, let’s look at the issues, but let’s not drive our country apart.”

Mr Salmond claimed the Westminster parties had got themselves into a “log jam.”

“David Cameron doesn’t think he can carry his own backbenchers, never mind the threat from Ukip, unless he links Scottish progress to changes in England.

“Ed Miliband doesn’t want to do that because Labour would lose their majority over English business in the House of Commons.”

Labour former chancellor Alistair Darling said there was a “bigger issue about what constitutional reform is needed” but the agreement reached by the three main parties was “non-negotiable.”

“The debate in Scotland is altogether more advanced and more developed than it is in other parts of the UK because we’ve had a referendum campaign,” he said.

Senior Scottish Cabinet members began to line up yesterday behind Mr Salmond’s deputy Nicola Sturgeon as the next leader of the SNP.

Finance Secretary John Swinney ruled himself out of the running and endorsed Ms Sturgeon as an “excellent successor.”

Education Secretary Michael Russell and Justice Secretary Kenny MacAskill also backed Ms Sturgeon, who has yet to declare her intention but has never hidden her wish to lead the SNP.