Britain could be kept in the European Union if more than a million foreigners living here are given a vote in the referendum, it has been warned.

Eurosceptic Conservative MPs want ministers to commit to allowing only British citizens to take part in the vote on whether the country leaves the EU.

There are worries that pro-Europeans will rig the result by insisting on including EU citizens living here. They are already allowed to vote in local and European elections but not general elections.

The Conservative Party manifesto promised that David Cameron (pictured) would negotiate new rules with the EU

The Conservative Party manifesto promised that David Cameron would negotiate new rules with the EU and ‘then put these changes to the British people in a straight in-out referendum on our membership of the European Union by the end of 2017’.

But there are concerns that Mr Cameron might water down this pledge because he wants Britain to remain inside the EU.

Liberal Democrats in the Lords could also join forces with pro-EU Tories and Labour to give foreign nationals a vote.

They could force through an amendment to the EU Referendum Bill so that the local government register is used rather than that used for general elections.

The Government has said it will decide on exactly who can vote when it publishes the Bill.

The electoral register for Westminster elections included 45.3million voters but there were an estimated 46.8million registered for local and European polls.

If the in-out referendum result is close, the votes of the 1.5million citizens of EU countries living in Britain could be decisive.

Tory MP Philip Davies said the Government ‘would never be forgiven’ if foreign voters made a difference to the referendum result.

He said: ‘Clearly they shouldn’t be allowed to vote and as far as I am concerned the Government is not proposing that they should, so we are on the same hymn sheet.

Labour leadership front-runner Andy Burnham (pictured) has increased pressure on Mr Cameron by demanding the referendum is held next year

‘Mine would be a warning shot across the bows of the House of Lords, if they try to use their Euro-fanatic majority there to try and overturn the will of the Government. As far as I can understand the Government are going to stick to the General Election register. Any attempt to change this will be unacceptable.’

Mr Cameron has said he wants to renegotiate the terms of Britain’s membership of the EU so that Britain gets a better deal with controls on immigration. He is then expected to campaign for the country to remain in the EU.

Foreign Secretary Philip Hammond, who is known to be Eurosceptic, last week said he wanted to campaign for an ‘in’ vote and raised the prospect of bringing forward the date of the referendum before the December 2017 deadline.

Labour leadership front-runner Andy Burnham increased pressure on Mr Cameron on Sunday by demanding the referendum is held next year.

Clearly they shouldn't vote

In a dramatic bid to outflank the Prime Minister, Mr Burnham declared he wants to change the Opposition’s policy to support a national poll on the key issue.

He also warned Mr Cameron he would be ‘held to account’ if he failed to negotiate a good settlement with Brussels that addressed concerns over immigration.

The intervention follows calls from Tory backbenchers for the referendum to be held earlier than 2017.

In an interview with the Observer, Mr Burnham said: ‘The country has voted now for a European referendum and under my leadership the Labour party will not be a grudging presence on that stage...

‘It should be in the Queen’s Speech that it should be in 2016, and the message I would send to Cameron is that I would offer support to deliver it in 2016. It is not going to be in anybody’s interest for this to rumble on through this parliament.

‘We have to get to it. We have to do it, embrace the argument. That is the most fundamental problem facing British business right now.’