THE SNP has been challenged by Labour to back a Tory amendment to the Scotland Bill, which has "called their bluff" as it would fast-track full fiscal autonomy(FFA) for Holyrood.

The amendment by veteran Conservative backbencher Sir Edward Leigh would seek quickly to hand over all powers to the Scottish Parliament on, among other things, finance, home affairs, trade and industry, energy, transport and social security; leaving matters like defence, foreign affairs and the constitution reserved to Westminster.

The SNP has put down its own amendment on FFA - set to be debated on the first day of the Bill's detailed committee stage on Monday - but its critics claim it is "a fudge" as it only hands the power to Holyrood to decide if and when it would operate full powers over tax and spending in Scotland.

They believe the Nationalist leadership has got cold feet on FFA following the calculation by the respected economic think-tank, the Institute for Fiscal Studies, that introducing it and scrapping the Barnett Formula would leave the Scottish Government with a £7.6 billion annual black hole.

The policy of FFA came under further attack this week when the Office for Budget Responsibility slashed its forecast for North Sea oil revenues, on the back of the oil price slump, to just £2.1 billion up to 2040; £34.5 billion lower than its forecast last year.

Labour's Ian Murray, the Shadow Scottish Secretary, said: "The SNP need to be honest with the people of Scotland about their plan for FFA. We need to know what timescale they want for it, how much they know it would cost Scotland and what spending cuts or tax rises they would make to close the extra £7.6bn gap.

"If the SNP really want FFA, they could deliver it by 10pm on Monday by voting for the Tory amendment in the Scotland Bill, that actually proposes it in full rather than the SNP fudge. We will find out then if they have the courage of their convictions."

Mr Murray called on the SNP to abandon what he called "full fiscal folly" and support Labour's amendment for a review on the full impact of FFA on Scotland's public services.

In response, Stewart Hosie, the SNP's deputy leader, said Nationalist MPs were looking forward to Monday's debate, stressing that the party was proposing to amend the Scotland Bill to give the Scottish Parliament "the ability" to introduce FFA.

Scotland, he argued, needed significant new powers over its economy, job creation, welfare, wages and living standards if the most was to be made of the nation's potential.

"Once again Tory and Labour politicians are working together to try and block meaningful additional powers for Scotland; that is one reason why they only have one MP each in Scotland.

"Labour's problem is that they would prefer to see a Tory government rather than the Scottish Parliament and people making decisions on key measures like our welfare system and the minimum wage. That is an absurd position for the Labour Party to be in," he added.

Other amendments to the Bill seek to:

*ensure Holyrood could only be abolished with the consent of the Scottish Parliament and a referendum in Scotland(SNP);

*ensure Westminster could only legislate in devolved areas with Holyrood's consent by putting the Sewel Convention on a statutory footing(SNP);

*set up a constitutional convention(Labour);

*require the consent of Holyrood to scrap the Human Rights Act as it applies to Scotland(Labour's Graham Allen) and

*ensure Holyrood nominates members of the House of Lords in proportion to Scotland's share of the UK population(Mr Allen).