Just to clarify the law regarding expat rights to vote in the forthcoming referendum:
"British expats who have lived outside the UK for less than 15 years qualify to be able to vote in the forthcoming referendum. They should immediately register to vote online if they have not done so already: https://www.gov.uk/register-to-vote."
Unfortunately those who have lived outside the UK for more than 15 years are not currently eligible to vote.