SNP MPs will vote on English health matters in the next parliament, Nicola Sturgeon has confirmed, in a move seen as positioning her party for a possible deal to prop up a minority Labour government.

The First Minister said her party's MPs would vote to limit privatisation in the English NHS - a cause championed by Labour.

She claimed the move would protect Scotland's budget.

However, her willingness to relax the SNP's self-imposed rule against voting on English issues will be seen as an attempt to pave the way for a possible power-sharing agreement.

Her comments came as an Ipsos MORI poll for STV News put the SNP 28 points ahead of Labour in the battle for Westminster seats.

It was the latest in a series of polls which suggest the Nationalists could hold the balance of power after May 7.

The Ipsos MORI poll found 52 per cent of voters planning to back the SNP compared to Labour's 24 per cent.

It would give the Nationalists 55 of Scotland's 59 seats at Westminster, up from six, while Labour would hold just four.

The Tories and Liberal Democrats would lose all their seats north of the Border.

Ms Sturgeon said: "The current Westminster agenda of austerity, privatisation and patient charging in the NHS in England threatens to harm Scotland's budget, on which our NHS depends.

"Therefore, SNP MPs elected in May are prepared to vote for a Bill which would restore the National Health Service in England to the accountable public service it was always meant to be.

"Such a step would be good for England by giving people their health service back - and also represent enlightened self-interest for Scotland, by protecting the Scottish budget from the cuts which English privatisation are undoubtedly paving the way for.

She added: "We want Scotland to be fully financially autonomous, but until that is achieved SNP MPs helping to reverse English health privatisation would be a vote in the Scottish national interest too."

Labour have pledged to repeal the 2012 Health and Social Care Act, which opened up the English NHS to widespread privatisation, if Ed Miliband becomes Prime Minister.

The party has also outlined plans to invest an extra £2.5billion - partly raised by a proposed mansion tax - in health, of which Scotland would receive a £250million share.

Scottish Labour leader Jim Murphy - who has played down the chances of a deal between his party and the SNP - dismissed Ms Sturgeon's comments.

He claimed the SNP were spending less on the NHS "than even David Cameron" and added: "There is a way of getting a better health service, a way of getting more money for Scotland's health service, and that is by voting for the Labour Party."

Scots Tory leader Ruth Davidson said: "The SNP had previously taken a principled stance on this matter but it now seems principle goes out the window if it means stitching together a coalition deal with Labour

"We need to be clear - the price of that SNP deal would be to put our defences at risk and tear up the stable tax and spend system which keeps Britain's economy secure.

"It also risks letting independence in by the back door."

Ms Sturgeon's comments are likely fuel Conservative demands for "English Votes for English Laws".

During last year's referendum campaign the SNP claimed privatisation of England's health service would lead to cuts in Scotland's health budget.

The claim was angrily rejected by the pro-UK Better Together campaign.

Figures from the IFS think tank showed that, despite increasing privatisation south of the border, public spending on health has been rising in real terms, while falling in Scotland.

In the Chancellor's Autumn Statement in December, the Scottish Government received an additional £120million as a result of increased health spending in England.