When I came out to Malta a year ago, registering to vote in the UK from abroad was a complicated process requiring one to find another UK passport holder here to countersign etc.
Seems all has changed, I have just registered under the new system. As long as you been away less than 15 years and you have a valid passport, know your UK NI number and remember the address in UK you were last registered at, it is fairly simple to register online for a postal/proxy vote.