An independent Scotland could delay increases in the retirement age, but this would be "costly to fund", a new report has said.

UK plans to increase the age at which people get the state pension could be deferred in Scotland, thanks to cheaper pension costs north of the border, a study by academics from Stirling University said.

But this could result in additional pension costs of about £550 million.

The experts stated: ''Our analysis has shown that the costs of the state pension would be lower in Scotland, due to Scotland's lower life expectancy.

''This could, in theory, be used to reduce contributions or to delay increases in the state retirement age in Scotland, relative to the rest of the UK.''

But it went on to warn: ''If there are many pensioners and few workers, then such a policy could still be costly to fund.''

The paper, by Professor David Bell, Dr David Comerford and David Eiser, also warned the Scottish Government's ''triple lock'' guarantee for pensions in an independent Scotland would ''eventually be unaffordable''.

The report was published as part of a special issue of the National Institute Economic Review, focusing on the economics of independence.

The Scottish Government has already pledged to continue paying the basic state pension at the current rate if there is a Yes vote in September's referendum

Ministers would keep the ''triple-lock'' guarantee to ensure the pension keeps pace with earnings and rising costs for at least the first term of an independent parliament in Edinburgh, with pensions promised to increase by at least 2.5% a year.

An expert commission would be established to consider the appropriate age threshold for pensions - with Deputy First Minister Nicola Sturgeon having already suggested this could see people in Scotland picking up their state pension earlier than those in the rest of the UK.

Speaking in Edinburgh, Prof Bell said: "State pensions are potentially cheaper in Scotland than they are in the UK as a whole on an individual basis. The reason pensions cost less on an individual basis in Scotland is due to Scotland's higher mortality, life expectancy being lower in Scotland than it is for the rest of the UK.

"There's a delay of 12 years before Scotland achieves the same life expectancy as pertains in the rest of the UK. Life expectancy is increasing - it is lower in Scotland, 12 years later it will have caught up.

"So should Scotland delay the introduction of an increase in the state pension age? That would have a real terms cost that we put at around £550 million over the 12 years."

The report, from Prof Bell and his colleagues, said it was ''between 6% and 8% cheaper to provide a pension to an individual given Scottish mortality experience than it is given UK mortality experience'', and added that it ''may well be actuarially fair to defer the rise in the state pension age in Scotland due to its heavier mortality''.

But it cautioned the ''triple lock'' policy would eventually become unaffordable.

''One of the policies to which the Scottish Government has committed to is the maintenance of the so-called 'triple lock' in state pensions after independence,'' the report said.

''This ensures that the state pension will increase by the maximum of 2.5%, the rate of growth of earnings, or the rate of growth of prices. This is a strong commitment which will eventually be unaffordable.

''The real costs of funding state pensions will rise particularly during periods of stagflation, when high rates of inflation are combined with low economic growth.''

It went on to state that the Scottish Government's commitment to the ''triple lock'' policy ''suggests a need to reassure voters that they will not experience significant losses as a result of Scottish independence''.

Ms Sturgeon said: "This research makes clear that the lower life expectancy in Scotland means it would be fairer for people here if the increase in the pension age was postponed.

"Indeed, the paper states that the optimal policy for Scotland would be a state pension age relatively lower than the rest of the UK.

"I have already made clear that we are concerned about Westminster's accelerated timetable for increasing the state pension age to 67. This is now planned to be delivered eight years earlier than originally planned, which unfairly disadvantages Scots.

"We want to make sure that the pension age suits Scottish circumstances - and, on average, people in Scotland have fewer years in retirement receiving the state pension because life expectancy is lower. Independence will allow us to tackle lower life expectancy in Scotland once and for all, but it is not fair for Scots approaching retirement age to suffer in the meantime.

"In the first year of an independent Scotland, we will establish an independent commission to consider the appropriate pace of further change to the retirement age beyond 66, taking account of Scottish circumstances. The commission would report to the Scottish Parliament within the first two years of independence, allowing us to take decisions which best suit the needs of people in Scotland nearing pensionable age."