Re: Freedom of movement.
"Ex-pat UK citizens do have a say in the referendum provided they've been registered to vote in the UK in the last 15 years."
Incorrect. You have a right to vote in the referendum or general election if you have been out of the country for less than 15 years on the day of the vote. (And are, obviously, registered to vote.)
You'd be surprised how many that rules out.
There was a private members bill late last year to remove the 15 year rule (which the conservatives had promised to do in their manifesto) but the MP I wrote to refused to back it on the grounds that the government had a bill that was mentioned in the Queen's speech last year but will not be tabled until after the referendum. (If at all.)
But don't let facts get in the way of a good rebuttal.