NICOLA Sturgeon has vowed to explain how she would use Holyrood's new powers regardless of whether a deal is done to approve the Scotland Bill before the election.

The First Minister called on David Cameron to intervene in the deadlocked negotiations over the "fiscal framework," the complex financial arrangements behind the devolution of extensive new tax powers.

She also tore up her previous February 12 deadline, saying she would do "everything in my power" to get a deal that MSPs could approve in time for the Holyrood election on May 5.

In a demonstration of her commitment to the new powers, she said:

"I want these additional powers.

"I've spent my entire adult life campaigning for a Scottish Parliament that is as powerful as possible.

"Let me be clear: whether or not a deal is struck before the election - and I hope a deal is struck before the election - my manifesto will set out how we would choose to use these powers.

"But for any party to use them meaningfully, we need a fiscal framework that is fair."

The SNP has come under growing pressure to say how it would use Holyrood's existing and possible future tax powers since Labour and the Lib Dems backed a 1p.

Some opposition MSPs have privately accused the SNP of  trying to stymie the talks in order to avoid difficult questions in the run-up to the election.

Speaking to reporters at her official residence, Bute House, Ms Sturgeon said a deal could only be struck if the UK and Scottish governments reached a "shared understanding" of the "no detriment" principle agreed by the Smith Commission, the body whose recommendations  formed the basis of the Scotland Bill.

It stressed neither Scotland nor the rest of the UK should suffer financially as a result of the decision to devolve powers, but the two government have failed to agree on what that means in practice.

Ms Sturgeon said the latest proposals from the Treasury would systematically reduce Scotland's budget by just under £3billion over 10 years.

She said: "I don't believe that anyone who signed up to the Smith Commission agreement did so believing it would result in a systematic reduction in our budget.

"It's not what the Smith Commission recommended and it is not what was promised to the Scottish people in the pre-referendum 'vow'."

In a letter to the Prime Minister, she said the Scottish Government was willing to accept "upside and downside" effects of taking control of income tax and other levies.

However, she said she would "not accept" Treasury proposals that would not maintain Scotland's funding if, as predicted, the country's population does not grow as quickly as England's.

She said the Scotland Bill would not give Holyrood "the levers that would allow us to grow our population at a faster rate".

In a separate move, Finance Secretary John Swinney called for greater "flexibility" from the Holyrood committee which will scrutinise any deal prior to a vote by MSPs.

A Treasury spokeswoman said: “The UK Government is absolutely committed to implementing the Smith agreement in full and in line with the no detriment principle.

"The offer we have placed on the table would have delivered more funding for the Scottish Government than the existing Barnett formula since devolution in 1999.

“From the outset our position on the fiscal framework has been clear – we stand ready to do a deal that is fair for Scotland and fair for the rest of the UK.”

Labour’s Shadow Scottish Secretary, Ian Murray MP, said: “We welcome this move by the First Minister. At the weekend, we asked both parties to set out the principles they are following, and we are glad Nicola Sturgeon has done that today. We also welcome her shedding light on the areas where both parties continue to disagree.

“We need a conclusion to this process that is fair to people in Scotland and that protects our public services now and into the future.

"We repeat our call today that Scottish and UK Ministers should not leave the negotiating table until a deal is done."