Two seats will be contested at the General Election where the majority of voters were born overseas.

A record four million people born abroad will be able to vote in May after a decade of mass immigration, a study predicted yesterday.

The figure – up 500,000 since the last election – represents one-tenth of the electorate.

In a historic development, more than half of those eligible to vote in London’s East Ham and Brent North seats were born overseas.

In two seats - East Ham and Brent North - more than half of voters were born outside the UK

In 10 areas outside the capital at least a quarter of voters are foreign born, according to the study

Such voters will make up a third of the electorate in another 25 seats, and at least a quarter in a further 50 constituencies, according to experts at Manchester University.

Their report says those born abroad are likely to hold the balance of power in 20 key constituencies – including 12 Labour marginals, six Tory seats and two held by the Lib Dems.

The country that provides the most foreign-born voters in England and Wales is India, followed by Pakistan, the Republic of Ireland and Bangladesh.

The figures, compiled for the Migrants’ Rights Network, include up to two million immigrants granted British citizenship since 2000.

About 200,000 applications are now approved every year – or one every two-and-a-half minutes.

Large numbers arrived when New Labour was operating an ‘open-door’ immigration policy – a strategy designed, according to Labour adviser Andrew Neather, to ‘rub the Right’s nose in diversity and render their arguments out of date’.

The 3.98million voters born overseas includes up to a million from the Commonwealth who do not have British citizenship.

Former Labour minister Barry Gardiner is the MP in Brent North while shadow minister Stephen Timms is MP for East Ham

Recent analysis by MigrationWatch UK, based on the 2011 census, showed there are 960,000 who have the right to vote in England and Wales.

Under arcane rules, citizens of 54 independent sovereign states can register on the electoral roll as long as they have an address in Britain.

In many cases, the arrangements are not reciprocal. Britons are not allowed to vote in Canada, Australia or the three most populous countries in the Commonwealth – India, Pakistan and Nigeria.

In 2008, a report commissioned by the then prime minister Gordon Brown called for changes in the rules to prevent Commonwealth nationals without UK citizenship from voting in general elections.

The report was never acted upon by the Labour Government – nor has the issue been addressed by the Coalition.

MigrationWatch has suggested that ‘one possible reason’ why Labour ignored the report was that minority voters are more likely to support the party.

WHERE FOREIGN BORN VOTERS COULD HOLD THE BALANCE OF POWER Top 10 seats in London Top 10 seats outside 10 London

East Ham 51.0% Leicester East 39.3% Brent North 50.0% Birmingham, Ladywood 34.3% West Ham 47.1% Slough 33.2% Brent Central 44.6% Leicester South 29.7% Ealing Southall 43.4% Luton South 29.6% Harrow East 43.3% Bradford West 29.1% Harrow West 43.0% Manchester, Gordon 27.2% Ilford South 41.6% Bimringham, Hall Green 26.4% Westminster North 40.5% Manchester Central 25.0% Cities of London and Westminster 38.9% Bimingham Perry Bar 24.6%

The Runnymede Trust, an anti-racism organisation, found that 68 per cent of these voters backed Labour in the 2010 election.

The Conservatives and Liberal Democrats received just 16 per cent and 14 per cent of their votes respectively.

The authors of yesterday’s report said that although migrants will not vote as a bloc, patterns suggest they are likely to prefer parties viewed as ‘positive’ about race equality and immigration.

They added that the growing significance of the ‘migrant vote’ is being largely ignored by the main parties.

Co-author Robert Ford told The Guardian: ‘Migrant voters are almost as numerous as current Ukip supporters, but they are widely overlooked and risk being increasingly disaffected by mainstream politics and the fierce rhetoric around immigration caused partly by the rise of Ukip.

‘Britain is more than ever an outward-facing, globalised country with a huge, hardworking, mobile electorate born overseas.

However, the political debate fails to reflect that contemporary reality in any meaningful way.

Ukip have made all the running with the immigration debate in the past few years and we have seen all of the parties looking to offer a harder line on migrants.

‘But there is another side to this debate – millions of hardworking British citizens who came to this country from abroad who find this kind of rhetoric profoundly alienating.

‘If the parties do not respond to that then they face lasting damage as this electorate is only going to become more significant.’

EU citizens are permitted to vote in local elections but not Parliamentary contests. This week, Ukip’s Nigel Farage said they should also be barred from any future referendum on EU membership.

Last night MigrationWatch chairman Lord Green of Deddington said: ‘This report underlines the absurdity of giving the vote in Britain to foreign citizens from Commonwealth countries which do not give the vote to British residents in their own countries.