New immigration statistics are out today, showing net migration to the UK has reached the highest level on record.

Ukip leader Nigel Farage had this to say:

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His question was echoed by this news website, among others.

What most have failed to mention is that there is a very simple reason why those two sets of figures mentioned by Mr Farage are so different: they measure completely different things.

Today’s quarterly migration stats from the Office for National Statistics do suggest a sharp increase in the rate of immigration from Romania and Bulgaria.

Some 53,000 Romanian and Bulgarian citizens immigrated to the UK in the year ending March 2015, almost double the 28,000 who came in the previous 12 months.

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This number represents just over 8 per cent of the total immigration to the UK in that period.

These ONS figures measure the flow of people coming in and out of Britain during certain periods of time, rather than a settled population.

But people who apply for a national insurance number within a given year haven’t necessarily arrived on these shores within the previous 12 months – they might have been living here for years.

Some 214,000 national insurance numbers were handed out to Bulgarians and Romanians in the year to June 2015, according to the Department for Work and Pensions (DWP).

That’s up from 129,000 in the previous year, although a change in the way registrations are recorded means this may be an exaggeration and the figures “should be viewed with caution”, DWP says.

But any recent surge in registrations is not evidence of a sudden influx of new migrants.

Rather, as the government literature makes clear, it reflects the fact that transitional employment restrictions on Bulgarian and Romanian workers were lifted on 1 January 2014, opening up the labour market to people from those countries who were already living in the UK.

It’s also worth noting that a student who comes to work in the UK for a couple of months over the summer before returning home might still get a national insurance number.

The two sets of figures do contain some interesting information: the ONS numbers show a big increase in the numbers of migrants who state their main reason to come to Britain as “work”, for example, while the DWP figures show a fall in the number of foreign nationals claiming working-age benefits.

But it’s difficult to compare them in the way Mr Farage does, because the DWP figures are not a measure of long-term migration. It’s apples and oranges.

Syrian migrants walk along a railway track to cross the Serbian border with Hungary near the village of Horgos

The bigger picture

Today’s ONS figures tell us there were 636,000 long-term migrants in the 12 months to March this year. Take away emigration and you get a figure of 330,000 for net migration, the highest on record.

The Conservative “ambition”, as laid out in the party’s 2015 election manifesto, remains to reduce net migration to “the tens of thousands, not the hundreds of thousands”.

Immigration minister James Brokenshire said: “These stark figures are deeply disappointing.

“While these figures underline the challenges we need to meet to reduce net migration, they should also act as a further wake-up call for the EU. Current flows of people across Europe are on a scale we haven’t seen since the end of the Second World War.”

The line about the biggest movement of people since World War Two has been used by the International Organisation for Migration among others, but in the specific context of illegal immigrants trying to get into various EU countries from trouble-spots like Syria and Afghanistan.

The figures are certainly stark: in July this year the EU detected more than 100,000 migrants at its borders, the biggest monthly figure since records began in 2008.

But it’s not clear what this has to do with today’s ONS figures, which only deal with legal immigration, and only take us up to March this year, before the widely reported problems at Calais and other recent border standoffs.

And it’s not clear that large numbers of the migrants who are making it into Europe and moving around are getting as far as the English Channel.

If every migrant who gathered at Calais this summer had been given permission to come into Britain, we would only have been talking about a total of about 5,000 people, according to local estimates.

Today’s ONS figures do show an increase in asylum applications to the UK, from 23,515 to 25,771 in the year ending June 2015, a 10 per cent rise.

But the numbers are well below the peak of 84,132 applications made in 2002 and are well behind applications made to Germany, France, Italy, Hungary and Sweden.

In the past the Conservatives have linked high net migration figures with EU membership, and eurosceptics will note that the proportion of EU citizens as a share of total migrants has been rising for some time:

Nevertheless, it remains the case that more non-EU citizens are migrating to the UK than EU citizens.

In fact, even if the European Union did not exist, net migration from outside its borders would still be higher than the “tens of thousands” promised by the Conservatives.