Net migration: Some say it's going up, others say it's going down - so who's right?

If you've been following the news today, you might have noticed something slightly odd in the coverage of the latest migration figures, just published by the Office for National Statistics.

Some people say net migration is going up. Others say it's going down. Raising the question: who is actually right?

The short answer is: probably a bit of both - but more of the former than the latter. But bear with me for the longer answer, because it's quite instructive, and will help you better navigate these numbers when they next come out. And, given we're talking here about historic quantities of migration, with profound consequences for the economy and the country more widely, it's certainly worth pausing for a moment over this.

The clearest way of understanding what's going on here is to note that when the ONS releases any figures, they're always subject to revision. Often an initial estimate can be drastically different from the eventual figure. That's certainly the case with migration statistics.

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To see what I mean, consider the answer to what should be a simple question: what was net migration in the 12 months preceding last June? This time last year, the ONS produced some data showing that it was 672,000 people.

Now, that was a high number - and caused some raised eyebrows, to put it lightly, at the time. However (and this matters), the ONS data showed back then that this 672,000 figure was actually a little lower than the previous quarter. It looked, in other words, as if migration was falling.

And so ministers could go out and say that net migration was falling. That, after all, was what the data suggested. But remember, that data was always provisional.

In the intervening period, the ONS discovered that more people than they previously thought were coming into the country. Fewer people than previously thought were leaving the country.

The upshot is that today the answer to that same question - what was net migration in the 12 months to last June - is different. It's not 672,000. It's 907,000. And far from falling at that point (as the ONS previously suggested) it was actually rising.

Who are the kinds of people coming?

There are a few important points to take from this. For one thing, the flow of people into this country is even bigger than previously thought. And it was previously thought to be pretty enormous. Never in British history have so many people come into this country.

It's worth at this point underlining that the vast majority of what we're talking about here is legal migration. It's not people coming across in small boats. It's people coming to the UK to study and to work.

Best to be cautious about recent data

The other point to take from this is to be quite cautious about the most recent migration data. Look at today's ONS figures and they suggest net migration is falling at an annual rate of 20%, down from that 907,000 figure to 728,000 in the year to this June.

And it does look from other sources of data - Home Office visa approvals for instance - as if immigration does seem to be falling. But then again, the ONS figures suggested six months ago that net migration was falling by 10% in the past year (you might recall government ministers and even newspapers repeating that line). Today the revised estimate for that same period is a fall of only 1%.

It's all a useful reminder that data - as clean-cut as it sometimes looks - is often somewhat more uncertain the more you look at it.