The report below by the Cross-Party Group On Overseas Voters examines how, within the current 15-year-limit on their voting rights, British citizens living abroad can be enabled to register and vote in UK elections more easily and in greater numbers:
MAKING VOTES COUNT: Enhancing engagement in the electoral process by British expatriates (Overseas Voters Report).
One key recommendation out of a total of six (refer page 16) to overcome the problem of poor turnout, is that the Electoral Commission should devote more resources to registering citizens living abroad and be given a target of 100,000 registered voters.
Here below then is a message from the Electoral Commission : UK expatriates – Time is running out to register to vote in the European elections.
If you are still qualified to vote in UK elections, help to build towards that 100,000 expatriate voter target by registering to vote from overseas guided by the Electoral Commission on www.aboutmyvote.co.uk, in good time also for the general election in 2015.
If you are disqualified or not by the 15-year-rule, demonstrate the hidden potential of the British expatriate vote by adding your supporting vote here in our on-line poll to remove this arbitrary limit on your voting rights.
Votes for Expat Brits blog 
May I point to a blog post submitted by Lord Norton:
http://lordsoftheblog.net/2014/03/22/enhancing-electoral-engagement-by-british-expatriates/
Although the 15-year rule is off the cards for now, I believe the best route to overturning it is to embrace the group’s report via the above site, and to put every effort into securing over 100,000 votes at the 2015 General Election.
Members from the House of Lords are very receptive to encouraging remarks, even out and out flattery!