Population Projections – Further Analysis

21 March, 2004

1. Further analysis of the Government Actuary’s population projections has revealed that the impact of migration on the projected population has been grossly understated.

2. According to Government Actuary’s press release issued on the 18 December [1]: “Of the projected 5.6 million increase [in the overall UK population] between 2002 and 2031, just under half (2.6 million) is due to projected natural increase (more births than deaths) and just over half (3.0 million) to the assumed level of net inward migration and other changes[2]”.

3. Detailed analysis shows that this statement is highly misleading. In fact the three million is just a count of the net number of first generation migrants (i.e. immigrants less emigrants) in this 29-year period. (103,000 for 29 years is just under three million). Children and grandchildren of these migrants have been counted in the natural increase figure and hence not attributed as being due to the effect of net inward migration.

4. It is, however, possible to estimate the impact of net migration on the population projections. The Government Actuary provides a “natural change” variant population projection which shows the projected population assuming no migration, that is no immigration and no emigration. By comparing the results from this model with the principal projections it is possible to calculate the overall effect of migration. It is also possible to calculate the effect if migration were to remain at the level of 158,000 per year. The results are given in the following table:


Population 2002

Population 2031


to migration

Natural Change only (no migration) [3]
Principle projrction (103,000 net migration)[4]


Current migration (158,000 net [5] migration)


5. It can therefore be seen that, without migration, the population would grow by just under one million. With migration at the 103,000 per year – the Government’s principal projection - the population will increase by 5.6 million by 2031 and the vast majority of this, 85%, will be due to net migration.

6. If migration continues at the level which it has averaged over the last five years, i.e. 158,000, the population will increase by 7.6 million by 2031 – 89% of the increase being caused by migration.


[1] Government Actuary’s Department release of 18 December 2003 – New United Kingdom population projections – available at http://www.gad.gov.uk/news/documents/2002-based_national_population_projections.pdf
[2] “other changes” refers to an adjustment made for “unattributable population change”. An adjustment of 27,000 p.a. has been made under this heading and it is due to continuing unexplained discrepancies between the 2001 census and annual population estimates. In practice the population can only change as a result of births, deaths and migration and as births and deaths are measured accurately the adjustment can only be due to migration. We have therefore included the impact of “unattributable population change” under the migration heading.
[3] From GAD ‘special case scenarios – natural change only’ available at http://www.gad.gov.uk/Population/2002/uk/wncouk02cc.xls.
[4] Figures are from the GAD’s principal projections available at: http://www.gad.gov.uk/Population/index.asp? v=Principal&y=2002&subYear=Continue. We have taken the net migration figure as 103,000 p.a. (130,000 p.a. GAD assumption less 27,000 unattributable population change) – see footnote ii.

et migration level, which has averaged 158,000 over the last five years is assumed to continue, no adjustment has been made for unattributable population change. Figures have been calculated by interpolating between the ‘high migration’ variant projections available as in ii and the natural changes only projections as in iii.

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