SCOTLAND'S ageing population will pose a major challenge in the coming decades whether the country remains in the UK or becomes independent, a new report has warned.

The National Institute of Economic and Social Research (NIESR) found an independent Scotland would face higher taxes to support its elderly population than if it remained part of the UK, on current trends. However, it said the difference was less than suggested recently by another think-tank, the Institute for Fiscal Studies, and should not be a decisive factor in the referendum.

The report came as an assessment from the body representing Scotland's accountants, ICAS, raised questions about an independent Scotland's ability to set its own tax policies in the early years after a possible Yes vote. Meanwhile, a poll out today showed a slight rise in support for independence, with 26% of Scots backing a split in next year's referendum.

The NIESR concluded that average income tax rates in an independent Scotland would have to rise to 1.4% above those in the rest of the UK by 2035 to support the ageing population, though the gap would narrow to about 0.8% by 2060.

But its report concluded: "This difference should not be a major consideration when taking the decision about independence as the additional costs of supporting the ageing population as an independent state are much smaller than the costs of the population ageing itself.

"Scotland will have to bear these costs whether is stays part of the UK or becomes independent."

Labour's shadow pensions minister Gregg McClymont said: "The facts on independence are simple - Scotland's population is ageing at the same time as our working age population is decreasing. An independent Scotland would face big tax rises or large spending cuts to address this demographic and fiscal reality."

The Scottish Government - which plans to increase immigration in the event of a Yes vote to help support the elderly population - said the report showed demographic change was a challenge "whatever the constitutional situation".

A spokeswoman said: "With the powers of independence we could take action to meet the demographic challenge by boosting participation in the economy and growing the working age population."

Meanwhile, a TNS BMRB poll of 1004 Scots, conducted last month before the SNP's independence blueprint was published, put support for a Yes vote at 26%, a percentage point higher than in October.

Backing for No was 42%, down a percentage point, while don't knows remained at 32%.