The prediction, by the Registrar General for Scotland, is in sharp contract with the views of the local authority, which is planning for a population boom.

Last week, Registrar General Duncan Macniven forecast that Scotland's population would rise by five per cent by 2031 but there would be winners and losers among local authority areas.

It is anticipated the population will increase in the other Lothian authorities — West Lothian (22 per cent), East Lothian (21.2 per cent) and Edinburgh (17.2 per cent) — and in the Scottish Borders (15.6 per cent). However, it is expected Midlothian will see its population fall by 4.4 per cent.

A Scottish Government spokesman explained: "In the Lothians, the population increase will be down to a combination of in-migration and more births than deaths. The projected fall in Midlothian is as a result of out-migration, despite the fact there will be more births than deaths."

The statistics, which are used by the government across a range of areas including funding, are based on trends of births and deaths. The spokesman agreed that the data may not reflect ongoing work being carried out by the local authority and other bodies to promote growth.

The Registrar General's prediction for Midlothian (2006 to 2031) suggests the number of children, aged under 15 years, will fall by 12.4 per cent, the working age population will decrease by 11.2 per cent but the number of pensioners will increase by 25.8 per cent.

The projection indicates that Midlothian's population will peak at 79,540 in 2009 and steadily fall away over the coming decades finishing at 75,813 by 2031.

A Midlothian Council spokesman said: "The GROS biennial update of population projections for local authority areas is based on recorded trends in birth and death rates and migration in the five-year period 2001-2006 and the decline in population, which is projected for Midlothian, is at odds with the large scale housing development, which is already committed and planned in Midlothian.

"GROS acknowledge that their projections are trend based, ie based on natural change and migration data recorded in the last five years, taking no account of the large scale housing development planned in Midlothian, and are, therefore, not policy-based forecasts of what the government expects to happen."