Scottish Liberal Democrat leader Willie Rennie has claimed plans to give extra powers to Scotland risk being held back by "forces of Conservatism" - including the Labour Party.

Mr Rennie also called on both Labour and the Tories to improve their devolution offers.

The Lib Dems have been pressing Labour to back their proposals to hand 100 per cent of income tax control to Holyrood. Labour warns the move could threaten the future of the United Kingdom, by damaging the principle of the pooling and sharing of resources.

Mr Rennie told a fringe meeting that the independence referendum had created an "enormous opportunity". For us who have feared the forces of constitutional conservatism..... This is a great chance to get constitutional reform across the UK," he said.

He added: "I think the Labour Party proposals need to be beefed up, I think they need to do more."

He also said the Tories had to increase their offer to and do more across the UK alongside David Cameron's proposed English votes for English laws.

"There is a big challenge for those parties. But there is also a challenge to the SNP to have a form of constitutional change within the UK. There is a challenge to all the parties to be bold but also to be sensible about the reforms, that means we can have a settlement for the long term. That is the way to challenge the forces of constitutional conservatism."

Last night SNP MSP Clare Adamson said: "People in Scotland will be used to the Lib Dems selling out their principles by now - but these latest comments simply beggar belief, given they are joined at the hip in government with these same 'forces of conservatism'."

Meanwhile, the Scottish Secretary warned the SNP are putting jobs at risk by continuing to argue for independence. Alistair Carmichael also attacked Nicola Sturgeon, suggesting she was not behaving as a proper democrat should, accusing her of appearing to tell 55 per cent of voters in the independence referendum that they were wrong.

Mr Carmichael told a question-and answer session at the Liberal Democrat conference that the referendum outcome would result in a number of constitutional changes across the UK.

But he added: "Unless and until the nationalists come and tell us that they accept the verdict of the Scottish people and we are not going to be returning to the referendum question, you will not get the necessary healing and - more importantly even than that - there will continue to be a cloud of uncertainty over business life in Scotland.

"You will not see the investment, you will not see the growth and you will not see the jobs coming here that are possible now in the exciting post-referendum era."