Britain's fast-growing migrant communities could swing the vote in key constituencies in the upcoming general election, the closest and least predictable in living memory.

A recent report states that in this election, one in 10 voters will have been born abroad - that's some four million people, roughly equal to the number of Ukip voters, who campaign against immigration.

The Migrants' Rights Network (MRN) says as politicians ramp up rhetoric over immigration to counter the surge in popularity of Ukip, they risk alienating migrant communities, who could hold the balance of power at the ballot box.

The migrants able to vote are mainly from Commonwealth countries such as India, Pakistan and Bangladesh.

"Migrants will potentially have the power to swing a number of marginal seats and in areas with very diverse populations and with heated debates about immigration that could be very significant. Those parties that are talking to that group of voters could find themselves brought to power on the back of that vote," said MRN's policy director Ruth Grove-White, who co-authored the report.

Widespread concern

Polls suggest immigration is a widespread concern among the British electorate, some of whom feel migrants have depressed wages, taken jobs from Britons and diluted the country's identity.

Both Labour and the Conservatives have seen support drift to Ukip, which is expected to win about 14% of the vote. This has pushed both parties to promise to take a tougher line on the issue in an attempt to woo back voters.

The red hot political rhetoric on immigration has not been lost on people in parts of the country where migrants make up a large percentage of the population, some of whom feel marginalised by politicians.

Ealing Central and Acton is one of London's most diverse constituencies and is shaping up as one of the city's most tightly contested seats.

"I think we have a very settled migrant vote here in Ealing Central and Acton, and I think they take pretty much the same view as I do - which is London cannot continue to survive without a pretty hefty number of immigrants coming here to help us run our services," said the sitting MP, Conservative Angie Bray.

"But at the same time they want to make sure it's properly controlled; they are after all here paying their taxes like all of us and what they want to make sure is there aren't people coming over here to in anyway take advantage so I would say that it's a message shared by all of us, whichever community you belong to, that we want to make sure that we have a fair but efficient immigration system."

'You can't lump all migrants together'

Bray's Labour opponent, Rupa Huq, is acutely aware of how diverse local voters are and the power they wield.

Huq said: "A seat like this - a sort of urban, stroke suburban London seat the migrant vote can't be discounted. But then at the same time, you can't lump all migrants together - because that covers vast numbers of different people. And in a place like London nobody is really indigenous. If you scratch the surface most people have got a bit of Irish in them or something."

According to the MRN report, two London seats may already have a majority migrant electorate and the migrant vote is big enough in at least 70 seats to have an impact.

While not voting as a bloc migrants do tend to prefer parties that they view as positive about immigration. With immigration to the UK continuing apace, politicians would be ill-advised to ignore their views, said Grove-White.

She said: "What we think though is that this is a way-marker for the future. Which should really act as an incentive for politicians to think about the way that our changing population will have an impact on politics into the future that if you have a more diverse population you need to reflect that in your messaging not just in the run up to May but for subsequent elections as well."