The optimism on here might be misplaced.
http://www.bbc.co.uk/news/uk-politics-42279408
http://www.bbc.co.uk/news/uk-politics-42279408
UK citizens who move elsewhere in the EU before Brexit day will have the right to stay in that country.
However after the UK withdraws, the freedom of movement principles will not be the same for UK citizens living in the EU as EU citizens living in Britain.
As Jon Worth, a UK citizen living in Germany, said: "I can still go and take a day trip to (Poland), or go on holiday to (Italy) unrestricted, after Brexit day.
"But I could not move to live in Italy or Poland without restriction."
So for people like Mr Worth, the only way to keep this freedom of movement would be to apply for a passport in the European country they are currently residing in.