Futurists tend to love demographic projections. They are as close as they ever get to predicting the future, because there’s simply so much population trends data out there, not to mention actuarial data, that once people have been born, the future shape of the population can be estimated pretty reliably. At least in theory. But with fertility levels changing decade by decade, an ageing population, and migration statistics – and assumptions – fairly unreliable, population projections are becoming as uncertain as other trends. In particular the arguments about migration seem to me to be embedded in a post-war discourse dominated by our particular post-colonial experience.

At the end of October The Office for National Statistics published projections (opens in pdf) that the UK population would rise to 65 million in 2016, and 71 million by 2031, although they were very clear that this was ‘trends based’ This week they expanded on this with a ‘high’ and ‘low’ projection: 75 million by 2031 at the top end, and double by 2081. The low estimate reaches 65 million by 2031 and starts to decline later. (News report here, data here in pdf, ONS chart from bbc.co.uk below).

ONS population projections

The first long-term assumption is that UK fertility rates will stay at their current level, of 1.84, for women born after 1990. This is higher than the ONS’s previous long-term assumption of 1.74. I blogged about this data a few months ago, and it’s worth noting that while fertility rates were 1.87 in 2006, just five years ago they were at 1.63 (a UK low). And that fertility rates are lower right across Europe, save for France. So the ONS has embedded a fertility rate which may be on the high side.

Secondly, it has assumed relatively high inward migration rates. Again, there are reasons to have some doubts. The ONS has recently published migration estimates, which suggest a net inflow of 190,000 in 2006, although the way that the data is collected in fairly approximate. Some critics have suggested that the ONS is under-estimating, but there’s a wider issue: the UK discourse on immigration is dominated by our post-colonial experince, in which people have tended to come from far poorer countries with much shared cultural heritage, and have then generally stayed.

But recent work by the European Bank of Reconstruction and Development, and published in its recent Transition Report, suggests that the behaviour of migrants within the EU is likely to be different; research it has done in the accession states found that migrants from there wanted to go back as their home economies developed. (Report here in pdf, news analysis here). As Ashley Seager commented in the Guardian, “After all, did the British Auf Wiedersehen Pet builders stay in Germany in the 1980s or return home when there was more work here?”.

The longevity figures are probably least open to argument, given the surge in longevity recently. But even here some of the recent work on obesity and other health-related issues (for example the Foresight report from last month) suggests it could change.