THE SNP Government's pledge of guaranteed annual state pension rises will mean the cost of them to taxpayers will rocket from the current £53 million a year to a "black hole" of more than £700m by 2050 if Scotland became independent, according to Scottish Labour calculations.

Gregg McClymont, the Shadow Pensions Minister, said as a result John Swinney, the Scottish Finance Secretary, would be faced with having either to raise taxes or cut public spending.

Scottish Labour said that the figures which Mr McClymont had obtained had been "verified by external experts" but did not say who they were.

The so-called triple lock on state pensions guaranteed by the UK Government in the Coalition Agreement means state pensions increase each year by the highest of three measures, inflation, the increase in earnings, or 2.5%.

It was introduced in 2010 to insulate pensioners from inflation but while Labour has said it would seek to maintain the UK-wide mechanism if it got into power in 2015, the Tories and Liberal Democrats have offered no guarantee they would want to continue it beyond the next election.

Mr McClymont said: "Scotland was already facing a pensions timebomb as the number of elderly people rises faster than the rest of the UK. Now these figures make clear that the SNP have created another black hole in Scotland's future."

The MP for Cumbernauld, Kilsyth and Kirkintilloch East challenged the SNP Government to set out how state pensions would be paid for should Scots vote for independence next year.

"We know that big corporations will get a tax cut and that oil companies won't have to stump up more, which means the money will either have to be found through a tax hike on hard-working families or cuts in spending on vital public services. Which is it?"

Mr McClymont stressed being part of the UK meant the burden of the higher costs of pensions in Scotland was shared by taxpayers throughout the whole of the UK.

"Scots work hard to put money aside for their retirement. Alex Salmond and John Swinney are wanting all of us to take a gamble on our future and use our pensions as the stake," he argued.

"We all know that in private John Swinney questions whether a separate Scotland can afford even the current state pension but in public he still refuses to come clean. It's time the SNP were honest with the people of Scotland."

A Scottish Government spokeswoman said: "John Swinney recently announced that pensioners in Scotland would benefit from stronger safeguards than their counterparts in the rest of the UK following a vote for independence and the triple lock will be retained to protect those pensioners in receipt of the basic state pension."

She added: "Further details will be published shortly."

A spokesman for Mr Swinney said: "The only threat to people's pensions comes from Westminster. Labour raided the pension funds and destabilised the system and the Tories refuse to commit to the guarantees we can deliver with a Yes vote and independence."