THE need to increase ­Scotland's working age population, a key part of Alex Salmond's economic plan, has been underlined by a new statistical comparison of the four UK nations.

Figures from the ­independent Office for National Statistics (ONS) showed the ratio of working age people to pensioners is due to fall below that of England by 2037.

In addition, Scotland's overall population is due to grow at a slower rate and, in a further indication of demographic pressures, the number of deaths will overtake the number of births sooner than elsewhere in the UK.

The figures emerged in a new compendium of ­statistics designed to provide like-for-like comparisons between Scotland, England, Wales and Northern Ireland in a range of economic and social factors.

It showed, at present, ­Scotland and England each have 32 working age people for every 10 pensioners.

However, the number in Scotland is set to fall to 26 by 2,037 compared with 28 in England.

The figures are seen as important because they highlight potential pressures on public finances and their ability to maintain pensions and other spending commitments.

Scotland's overall population, now approximately 5.3 million, is expected to grow by nine per cent by 2037, compared with 16 per cent for England according the ONS's central projection.

The figures confirmed that Scotland is likely to rely on migration to boost numbers because, on current trends, the number of deaths will outstrip births in 2032. In Wales the year is 2034 but in England the birthrate is not due be overtaken by deaths in the coming decades.

Alex Salmond last week set a target for net ­migration, the difference between the number of people moving into and leaving Scotland, of 24,000 per year, in the event of Yes vote.

The figure compared with an average annual net migration, including people moving to Scotland from the rest of the United Kingdom, of 22,000 between 2001 and 2011.

Mr Salmond's plan, to be achieved by allowing ­overseas students to stay and work and targeting skilled foreigners and expats wishing to return, is part of a package of economic measures designed to increase tax revenues by £5 billion by 2030.

A Scottish Government spokesman said the ONS figures confirmed Scotland's recent average net migration figure of 22,000.