Expats can really make a difference in British politics if they register to vote in elections.
The Electoral Commission is running a global campaign to encourage expats who have not been out of the country for more than 15 years.
If these voters lived in marginal constituencies before leaving the UK, as few as 90 voters could swing the seat in the next general election, expected in May 2015.
The BBC has just put together an interactive table of the 49 most marginal constituencies which are likely to decide the election.
The research shows the greater number of constituencies stay with their incumbent party in an election and the result is really decided by changes in the marginals.
Marginal seats
Thurrock, Essex, is held by the Tories with a slender 92 vote majority.
If just a few expats registered and voted for Labour or the Lib-Dems, the seat would swing away from the government.
Adding up the total small majorities for the 49 marginals on the list shows 29,545 extra votes would swing all the seats to a different party.
This does not take into account voters living in the area changing their votes.
Around 5 million British expats live permanently outside the UK in more than 100 countries, and many cannot vote in the UK because of the 15 year limit that disqualifies them from taking part in elections.
The way the system works, expats register to vote in the constituency where they lived before leaving the UK.
How to claim your vote
To sign up, go to the About My Vote web site run by the Electoral Commission, enter your former post code and follow the instructions to sign up.
For details of the BBC marginal seat research, look up the interactive guide on the BBC News web site.
The Electoral Commission is lobbying to scrap the 15-year voting rule for expats.
To urge Parliament to support their cause, they need 100,000 expats to register to vote. Around 30,000 are currently listed as voters in local and general elections.
Many nations already let expats vote without any time limit on their absence from home.
They include the United States US, Switzerland France, Germany, Italy, Portugal and, Spain.
Campaigners Votes for Expat Brits are also urging expats to take up their right to vote and for abolition of the 15-year rule.
“We want to draw attention to the scandalous denial of voting rights to expats who have lived outside the UK for more than fifteen years,” says the group.
“We believe all expats should participate fully in the political process in their home country, by having unrestricted voting rights in national elections.”
