The report highlights births and migration as key factors

Findings from the General Register Office for Scotland (Gros) are at odds with previous estimates of a drop below five million by 2036.

The changes are being put down to a recent rise in births and migration.

This could lead to a population of 5.4 million in 2031, which is above the previous peak of 5.24 million in 1974.

'Ageing nation'

A drop in the number of people living in Scotland is still expected but at a later date.

The population is not now projected to fall below five million until 2076.

Registrar General Duncan Macniven said: "The recent upswing in births and migration has paved the way for continued gradual increase in Scotland's population until it reaches almost 5.4 million in 2031.

"We will still be an ageing nation in 2031, we expect there will be 18 people over 75 for every 10 today."

The report also predicts that the number of children aged under 16 will fall from 920,000 in 2006 to 860,000 by 2031.

An increasing population has the potential to boost Scotland's economic growth and help our nation prosper John Swinney Finance Secretary

The number of people of working age is projected to increase slightly from 3.21 million in 2006 to 3.23 million in 2031 but the number of pensioners could rise by about 31% to 1.29 million.

The number of people aged 75 and over is projected to increase by about 81% to 690,000 over the next 25 years.

By 2031, 67 out of every 100 people will either be children under 16 or people of pensionable age.

Cabinet Secretary for Finance and Sustainable Growth, John Swinney, welcomed the new projections.

He said: "An increasing population has the potential to boost Scotland's economic growth and help our nation prosper.

"Although we must not be complacent, a larger working age population can enhance the productivity of our economy and create increased consumer demand.

"As a result, the more optimistic picture painted by the registrar general will help this government meet its aim of increased and sustainable economic growth in Scotland."