Theresa May said on Thursday that she would offer EU nationals that have lived in the UK for five years or more the right to stay in Britain after Brexit, on the condition that equivalent arrangements are made for Brits living in the EU.

It’s worth saying before we start that some of the official figures on how many people are coming to Britain each year are disputed.

FactCheck looked at this debate before last year’s referendum. At the time, Jonathan Portes, Principal Research Fellow at the National Institute of Economic and Social Research, pointed out that there is a big difference between the official figures and the numbers of migrant workers registering for a national insurance number each year.

But we still have some interesting and reliable estimates from the Office for National Statistics on people that are already settled in the UK.

Here are five things we know about EU migration courtesy of that data.

1. Work is the main reason that EU migrants come to the UK

Of the EU migrants living in the UK in 2015, nearly 1.5 million had come to Britain for work reasons. Just over 800,000 came to join or accompany their spouse or child. A further 300,000 came to pursue formal studies here. More than a quarter of a million came to Britain for “other” reasons, including people who came to get married, to seek asylum, or to visit.

It’s worth saying that the figures above are not annual flows of new migrants. Rather, they are estimates based on a survey of people who already live in Britain, conducted each year by the Office for National Statistics.

2. Poles are by far the largest non-British group in the UK, and Indian nationals are second.

There were nearly a million Polish nationals living in the UK in 2015. Among non-British nationals, Indians make up the second largest group, followed by Irish nationals.

Again, these are not annual increases, but represent the non-British nationals already living in the UK in 2015.

3. 13 per cent of people living in the most pro-Remain area of Britain are EU nationals

Apart from Gibraltar, where over 95 per cent of voters opted to stay in the EU, the London borough of Lambeth was the most strongly pro-Remain in the country in last year’s referendum. Over 78.6 per cent of voters chose to stay.

13 per cent of the local population of Lambeth are EU nationals, with British nationals making up 78 per cent.

4. 21 per cent of people living in the most pro-Leave area of the UK are EU nationals

The town of Boston in Lincolnshire was the most pro-Leave area of Britain in the EU referendum, with 75.6% voting to end the UK’s membership of the trade bloc.

21 per cent of people living in Boston in 2015 were EU nationals, with 78 per cent British nationals. Less than 1 per cent of people in Boston were non-EU nationals.

5. Believe it or not, the most pro-Leave and the most pro-Remain areas of the UK have the same proportion of British nationals.

Despite the massive differences in the way they voted last year, 78 per cent of the populations of Lambeth and Boston are British nationals. But Boston has proportionately more EU nationals – 21 per cent, compared to Lambeth’s 13 per cent.

Compare that to the national average, which is around 5 per cent of the total population – as shown in the chart below.