DOWNING Street yesterday raised the prospect that David Cameron would give more details about which extra powers he might be prepared to see devolved from Westminster to Holyrood, as the SNP insisted it was his "democratic duty" to do so.

Last week, on a visit to Edinburgh, the Prime Minister suggested that if Scots voted no to independence, then he would consider more devolution; a move seen as a bid to outflank Alex Salmond and neutralise the devo-max issue.

Mr Cameron said in a speech: "When the referendum on independence is over, I am open to looking at how the devolved settlement can be improved further, and, yes, that means considering what further powers could be devolved."

The PM refused to elaborate, insisting the independence issue had to be dealt with before that of how "to improve the devolved settlement" could be discussed.

"That must be a question for after the referendum, when Scotland has made its choice about the fundamental question of independence," he declared.

This prompted a sharp response from the First Minister, who said Scotland would not be fooled again by promises of jam tomorrow; a reference to ex-Tory premier Sir Alec Douglas-Home, who in the 1979 devolution referendum urged Scots to vote no "for a better deal".

Mr Salmond insisted: "He should spell it out now so we can have a clear debate on the alternative futures for Scotland."

Yesterday, it seemed No 10 was beginning to ease its hard line. Asked if the Prime Minister would spend the next two years before the independence referendum continuing to stonewall on what he meant by extra powers, his spokesman said: "No. There is a Scotland Bill going through Parliament, which is already devolving powers to Scotland and we are also having a consultation on the referendum. No doubt, there will be plenty of opportunity to discuss these matters in the coming weeks."

Last night, the SNP maintained the pressure on Mr Cameron to set out the terms of his "offer" of more powers for Holyrood before the Scottish Government's consultation on the referendum ended on May 11.

"After claiming that more powers for Scotland are 'on the table', the Prime Minister now has a democratic duty to set out exactly what is on offer," declared Angus Robertson, the SNP leader at Westminster.

"People in Scotland are entitled to know whether his proposals include any real economic powers and responsibilities, for example, over welfare issues," he added.