A general election is looming - most guesses are for early May. If you live outside the UK or are likely to be outside the country at that time, register for a proxy or postal vote NOW before it's too late! You complete a form and send it into the electoral officer of the council of your last place of residence in the UK (assuming that was in the last fifteen years). Surprisingly (perhaps), they're pretty efficient about receiving the forms and processing them. The most difficult thing can be finding another UK citizen who can countersign your first application...
Details are here: http://www.aboutmyvote.co.uk/register_to_vote/british_citizens_living_abroad.aspx
In practice, it's better to appoint a proxy than get a postal vote: the timeframe available for postal votes is ludicrously short and it won't get there in time. IIRC, each party has someone in each constituency in which they stand who will act as a proxy (to vote for their party only!) at your request.
I'm not exactly sure it's actually fair that someone who doesn't live or pay tax in the UK votes in UK elections when there are plenty of people who live and pay tax in the UK that can't vote, but the system is what it is, so...
