SCOTTISH Labour have accused the SNP of betraying the Smith Commission, which is attempting to broker a deal on further powers for Holyrood.

Interim leader Anas Sarwar ­yesterday launched a strongly worded attack on the nationalists after senior figures dismissed Lord Smith of Kelvin's cross-party talks.

He urged the SNP to negotiate in good faith and respect September's vote to remain in the UK. A number of leading nationalists used their party conference in Perth last week to pour scorn on the Smith process, devised by the pro-UK parties in the run-up to the independence referendum.

MSP Christine Grahame told a fringe meeting: "The Smith Commission will not do anything for us," before urging activists to step up street campaigning for independence.

Another SNP MSP, Christina McKelvie, said: "We've got the Smith Commission. Great! They appointed a lord to tell us what we need. I hope the Smith Commission delivers. I'm not that confident it will."

Mr Sarwar said: "The SNP are part of the Smith Commission, but already they are sending their outriders to predict its failure.

"This is not only a betrayal of the Smith Commission process but a betrayal of all those Scots who voted for a stronger Scottish Parliament as part of the UK.

"The Smith Commission will deliver extensive new powers to the Scottish Parliament as was promised during the campaign The people of Scotland want politicians to work together, in good faith, to get the best deal for Scots.

"They want the referendum result, and the process we agreed, respected and carried through."

Lord Smith plans to publish his recommendations on further devolved powers at the end of the month, following five weeks of talks involving five Holyrood parties - the SNP, Labour, Conservatives, LibDems and Greens.

The commission's remit is to deliver more financial, welfare and tax powers with the aim of "strengthening the Scottish Parliament within the United Kingdom".

The SNP, who are ­represented in the talks by Finance Secretary John Swinney and MSP Linda Fabiani, insist they are taking part in good faith and accept their call for "devo max", or giving Holyrood control over all policy areas bar defence, foreign affairs and the currency, is unlikely to be accepted.

However, they have been accused of setting the ­eventual outcome up for a fall by misrepresenting promises made by the main UK parties in the days before the referendum.

In particular, they have seized on comments by former prime minister Gordon Brown, who promised "a modern form of Scottish home rule" and a devolution settlement "as close to a federal state as you can be in a country where one nation is 85 per cent of the population".

Mr Swinney has claimed the pledge goes "way beyond" existing proposals from the main UK parties.

Alex Salmond, meanwhile, has claimed Scots are "absolutely fizzing about what looks like a preparation for a betrayal of a solemn commitment made".

The latest row comes after new SNP leader, Nicola Sturgeon, told the party conference broken promises on devolution would bring independence closer.

It was among a number of scenarios, she suggested, that could shift public opinion in favour of a second referendum.

Addressing the conference on Friday, new deputy leader Stewart Hosie said: "Remember what it was they told the Scottish people, many of whom voted No to get more powers: 'The closest thing to a federal state within one to two years.'

"Let's make sure they deliver that promise and let's do it by delivering a record number of SNP MPs next year. That's the raw power Westminster understands. That's what Scotland needs to deliver next year."

Dismissing Mr Sarwar's attack, SNP MSP Rob Gibson said: "The SNP is now fully engaged with the Smith Commission and will hold the Westminster parties to account on their promises.

"The people of Scotland fully expect more powers and if these promises are broken the Westminster parties will find themselves paying a hefty price at the ballot box next May."