A map of Europe by the number of immigrants in each country

Immigration has consistently been cited as one of the most important factors for people who voted for Brexit.

While many who voted Leave hope that Britain's isolation from the EU can help to reduce net migration figures, maintaining access to the single market may mean having to keep open borders.

This map from Jakub Marian, based on UN data, shows the percentage of immigrant populations across Europe.

As some have pointed out, the high figures in Switzerland (29.6 per cent) and Norway (14.4 per cent) help to show that being out of the EU does not necessarily mean low net migration.

Both countries sit outside the union but have been made to maintain open borders as a trade off for access to the single market.

For all Theresa May promises to get net migration into the low tens of thousands, that probably won't be possible if the government still wants access to the world's biggest trading bloc.

As Open Europe points out: "If the UK had the same net EU immigration rate as Switzerland, it would mean nearly 400,000 more EU migrants a year."