Iain Gray, the Scottish Labour leadership contender, accused the First Minister of demeaning the Scottish Parliament and claimed that he could beat him by bringing an end to the “playground abuse” at Holyrood.

The former enterprise minister began his campaign to lead Labour in Scotland by promising a different style of politics from that offered by Alex Salmond: “I'm not going to suggest to you that I can outdo Alex Salmond on the playground abuse approach to politics,” he said. “I don't think that's how our politics should be. In fact, I think that much of the language and approach that the First Minister takes to our Parliament is actually quite demeaning for that Parliament.”

He added: “I would bring to it a very serious examination of what the SNP are actually doing.”

Mr Gray started his campaign for the Labour leadership at Prestonpans Labour Club in his East Lothian constituency. He used a speech to Labour activists to make a scathing attack on the SNP. Mr Gray said: “The SNP are not just breaking promises. They are breaking the promise of the next generation. They are not just letting people down. They are letting Scotland down.”

He also jettisoned Wendy Alexander's policy of demanding an immediate referendum on independence despite publicly backing the plan this year. He said: “We do not fear the verdict of the people but the SNP referendum is rigged. The question is rigged and the timetable is rigged. We should not support it.”

Mr Gray went on to insist: “I am as Scottish as Alex Salmond. But I see my country differently.”

Defending the future of the Union he added: “We are stronger together.”

As well as being a former minister in the Scottish Parliament, Mr Gray worked as a special adviser to Alistair Darling during his time as Scottish Secretary, prompting claims from his critics that he would be Westminster's man. Mr Gray denied that was the case, pointing out that during his time as a Westminster adviser he devolved more power to Holyrood over railway infrastructure. He also said that the leader of the Scottish party would have a powerful mandate after a vote of all party members as well as MSPs, MPs, MEPs and trade unions.

He went on to heap praise on Gordon Brown, describing him as “the best Chancellor in living memory” and adding: “He is still the best person to lead the Labour Party and I believe he will.”

Mr Gray's campaign appears to be slick and well organised and he was the first of the three main contenders to make it clear that he would challenge for the job after Ms Alexander's resignation.

He faces stiff competition from two other former ministers. Cathy Jamieson began her leadership campaign this week.

Ms Jamieson called yesterday for a windfall tax on energy firms after Centrica, the owner of British Gas, announced a 35 per cent rise in gas prices: “The Chancellor of the Exchequer should make it clear that unless we see these companies show some decency then he should be prepared to introduce a windfall tax and then use that money to reduce people's energy bills,” she said.

Andy Kerr, the former health minister, will start his leadership campaign today. Meanwhile, Ken Macintosh, the East Renfrewshire MSP, announced that he had pulled out of the leadership race and was backing Mr Kerr. He said: “Not only do I agree with him on policy issues, I know Andy has the experience and the spark needed to highlight the weaknesses of this divisive SNP government.”

Charlie Gordon, the Glasgow Cathcart MSP, has yet to decide if he will run. Des McNulty, the former communities minister, announced last night that he had pulled out of the race for the deputy leadership and would back Johann Lamont for the job.

Mr McNulty said: “I stated from the beginning that I would not stand as part of a joint ticket. On that basis I have not been able to secure sufficient nominations to proceed.”

Times Recommends

• How I lost the gift of joy for a while
• Why Ann Widdecombe has got it wrong
• Alas, it’s the end of the road for petrolheads