Labour has urged the SNP to back their calls to dump pre-devolution debt and continue the fight to block trade union reforms in Scotland.

Union Unite has called for an amnesty on all debt accumulated prior to the creation of the Scottish Parliament, to reflect their belief that devolution was intended to be "a fresh start".

Scottish Labour leader Kezia Dugdale said if the SNP is serious about ending austerity it will support Unite's plan, in a speech to the first ever Unite Scottish policy conference.

Ms Dugdale also accused the SNP of "sitting on their hands" and allowing the Trade Union Bill to be enforced in Scotland, after Holyrood's Presiding Officer Tricia Marwick said the Scottish Parliament is powerless to veto the Bill.

Ms Dugdale said that at Dundee City Council the equivalent of 55p from every pound raised through council tax is being spent on servicing pre-devolution debt.

She said: "This is a council which has just offered thousands of voluntary redundancies, and scrapping the pre-devo debt could save as much as £36 million over the next three years.

"Devolution was to be a fresh start, a new beginning and yet this historic interest is still a millstone around the neck of councils who are facing Scottish Government cuts.

"If the Scottish Government were serious about ending austerity they'd make the case right now for the interest on this debt to be dropped."

Ms Dugdale said it is within the Treasury's gift to write off pre-devolution council debt, which currently stands at £2.5 billion with an annual interest of 7% to 8%.

Asked if she had discussed Unite's proposal with former Labour chancellors Gordon Brown or Alistair Darling, she said: "I met Unite to discuss this on Tuesday of this week so no, I haven't.

"But I don't need to speak to them to believe there is a compelling case for doing this.

"I think Unite's document makes a compelling case for why we should go collectively to the Treasury to ask that this debt interest be written off."

Ms Dugdale also said she has legal advice which suggests Holyrood can change its standing orders to block the Trade Union Bill, without straying beyond its devolved competence as set out in the Scotland Bill.

She said: "If the standing orders don't allow for a Legislative Consent Motion - let's change the standing orders.

"The Scottish Parliament is in full control of its standing orders. Any committee or any organisation that has standing orders, the governance structure allows it to amend its standing orders.

"Thomsons' Solicitors advice is that this is the right thing to do. The advice that we have is that this is definitely an avenue worth pursuing, and I will pursue every avenue that I have to stop this Bill."

The SNP said it was "hypocrisy" for Ms Dugdale to suggest the SNP needs to act now, "given that it was Labour that drew up and established the 1999 Devolution Settlement and could have cancelled this debt at the time".

A party spokeswoman also said Labour had voted to leave trade union law powers in David Cameron's hands, "instead of allowing the Scottish Parliament to take a new and better approach".

A Scottish Government spokesman said: "There is clear opposition across Scottish society to the UK Trade Union Bill and the Cabinet Secretary for Fair Work, Skills and Training met with the STUC this week to discuss what more can be done to block the Bill or, should it be pushed through, how to mitigate the damage it will cause.

"The Scottish Government has lodged a further memorandum on the Bill with the Scottish Parliament and its consideration by the Devolution (Further Powers) Committee will provide an opportunity to properly consider the Bill on a parliamentary platform. However, the only way to truly protect workers in Scotland is to fully devolve trade union powers."