We can have mass migration or we can have affordable housing. But it’s hard to see how we can possibly have both. That’s the obvious implication of the revised long-term population projections released this week by the Office for National Statistics (ONS).

According to the ONS’s projections, in the 15 years from 2021 to 2036, the population of the UK will increase by 6.6 million. Net migration accounts for a staggering 92 per cent of this – 6.1 million people, with emigration of 7.6 million more than offset by immigration of 13.7 million. This averages out to net migration of 405,000 per annum. Which is remarkable in itself, given that the ONS’s most recent set of projections predicted that the total would be below 250,000.

Over the next 15 years alone, net migration is set to add the equivalent of five more Birminghams to the UK

These projections are, however, frontloaded. According to the ONS, net migration is set to remain at over half a million until 2026, before levelling off to around 315,000 per annum from 2028 onwards. This might seem like a substantial fall – a return to sensible levels after net migration of 745,000 in 2022. But this new ‘long-run rate’ of net migration is still a huge number. In fact that 315,000 figure is higher than in any calendar year before 2021.

To put it another way, over the next 15 years alone, net migration is set to add the equivalent of five more Birminghams to the UK – one every three years on average. In fact, 6.1 million people is 70 per cent of the way to another London. It also represents a dramatically increased rate of population churn, given that cumulative net migration in the previous 30 years totalled 5.4 million people. In other words, our population is set to change shape more than twice as fast.

It’s important to recognise the limitations of these figures. They are projections based on recent data (mainly migration trends over the last 10 years, with some input from a panel of experts). They are not forecasts. They do not incorporate predictions or assumptions about what might happen, in particular due to future policy changes. They don’t even fully reflect the package of measures announced by the government in December to bring down the numbers.

But if these projections are wrong, they’re just as likely to be too low as too high – in fact, significantly more so. Pretty much every migration projection by the ONS since 2010 has fallen short of actual numbers, and has been revised upwards. Who’s to say 315,000 might not be just as much of an underestimate as the old figure of 245,000 was?

This really does matter. Long-term population and migration data is at the heart of policy-making and planning right across government. If the projections are out, so are a lot of other things.

As we’ve seen from Office for Budget Responsibility reports, the ONS net migration projection is a significant variable in Treasury forecasts. Rightly or wrongly, it’s positively linked to GDP growth rates, which in turn matter for tax and spend, the Chancellor’s fiscal headroom under his debt rules, and hence the mood in the bond markets. So the revised figures will make for happy reading for Treasury mandarins at least.

Another crucial area in which migration figures are used is housing policy. And here there is no reason for anyone to rejoice. As things stand, the government assumes we need to build 300,000 homes in England per annum just to stand still – let alone do anything to alleviate the housing crisis.

In Centre for Policy Studies analysis back in November, we found that, at 2022 rates of net migration, we needed to build half a million homes, according to the government’s own formula. (Spoiler warning: we didn’t. In fact, we built less than half that.)

If you plug in these new migration projections, and adjust for the difference in population between England and the UK, you find that the housing stock will need to expand by more than 5.7 million homes over the next 15 years, with net migration accounting for 41 per cent of this figure (2.34 million homes). The official housing target for England, therefore, actually needs to be 382,000 homes per annum.

And remember, that’s just to stand still. Our previous analysis found that the housing deficit, which was already cavernous, had widened by 1.34 million homes in the decade from 2013, with immigration accounting for 89 per cent of this. Backfilling that deficit – and the cumulative deficit from previous decades – is going to be hard enough without immigration at even higher levels than in the 2010s.

It’s also important to bear in mind the distribution of immigrants within England. PAYE data suggests that non-EU migrant workers represent a huge share of employment growth in the UK – and roughly 30 per cent of them are ending up in London. The fact that a host of Northern and Scottish universities have set up satellite campuses in London, to attract international students, indicates migrants on student visas are concentrating themselves in the capital too.

Migration, therefore, is adding to housing pressures precisely where the housing crisis is already the most intense. This disproportionately affects younger workers, especially London graduates, who have yet to get a foot on the housing ladder, and for whom the dream of home ownership (and starting a family) is fading away before the onslaught of ever-rising rents.

We need more homes all across the country – greenfield and brownfield, urban and rural, north and south. But it is grimly ironic that the demographic who are most desperate for housing are also by far the most supportive of immigration – when it is historically high levels of net migration that are making the housing crisis they face so much more acute.