David Cameron is under fresh pressure over Europe after 95 Tory MPs said parliament should have powers to veto laws from Brussels.
The backbenchers have written to the Prime Minister saying the Commons should have the authority to block new EU legislation and repeal measures that threaten Britain's "national interest".
According to the Sunday Telegraph, signatories to the missive - drafted by senior MP Bernard Jenkin - include James Clappison, Conor Burns, John Baron, Anne Main and former defence minister Sir Gerald Howarth.
Another six apparently support the proposal but have not added their names - some because they are in government jobs.
Parliament currently has no automatic veto over EU laws, and the Prime Minister can only use the UK's veto to head off new rules in the most sensitive issues - such as defence and the budget.
A committee of MPs which scrutinises EU laws last month recommended that a national veto be introduced.
And the MPs' letter, sent to the Prime Minister this weekend, called on Mr Cameron to adopt the policy.
"Each time you have stood up for British interests in Brussels, you have achieved a great deal," it said.
"Building on your achievements, we would urge you to back the European Scrutiny Committee proposal and make the idea of a national veto over current and future EU laws a reality."
The letter stated that a new national veto over EU laws would "enable Parliament to disapply EU legislation, where it is in our vital national interests to do so".
It added: "This would transform the UK's negotiating position in the EU."
The letter said the veto - which would require a new Act of Parliament - could be used to deliver key reforms to Britain's relations with Europe.
That could include gaining control over immigration from within the EU.
In their letter, the MPs praised Mr Cameron for his insistence that national parliaments, not bureaucrats in Brussels, are "the true source" of democratic legitimacy in the EU.
"However, clarity about how we will achieve these objectives is vital for our credibility," the letter says.
Mr Jenkin, chairman of the Commons public administration committee, said the identities of all 95 formal signatories are included in the letter but most of the names are not intended to be made public.
In an article for the Sunday Telegraph, he wrote: "The privately declared supporters of this letter represent more than half the back benches.
"We speak for the mainstream of the modern Conservative Party in Parliament and in our constituencies, and for the voting public, both in the UK and throughout Europe."
A Number 10 spokesman said: "The Prime Minister set out his approach in his Bloomberg speech.
"He has already won his battle over European bank bailouts, cut the EU budget for the first time and launched a landmark debate on the future of freedom of movement.
"The Prime Minister is also the only one of the three main party leaders committed to giving the British people an in-out referendum on membership of a reformed EU.
"We will of course study this idea closely. But we need to look at what it would mean in practice.
"We've always been clear that Parliament is sovereign and more power for national parliaments must be a key part of a new settlement, including a 'red card' power so groups of national parliaments can block unwanted EU interference.
"But if individual national parliaments regularly and unilaterally overturned EU laws the Single Market wouldn't work, and even a Swiss-style free trade deal with the EU wouldn't be possible.
"It is important to negotiate a new deal for Britain in the EU and then put the choice to the British people: stay in the EU on new terms or leave altogether."
In an interview with the Sunday Times, Work and Pensions Secretary Iain Duncan Smith said he would like EU immigrants to have to wait for up to two years to claim benefits - rather than the current period of three months.
He said he had been speaking to other member states such as Germany, Italy and the Netherlands who were supportive of the idea.
According to Mr Duncan Smith, Britain should ask migrants to "demonstrate that you are committed to the country, that you are a resident and that you are here for a period of time and you are generally taking work a nd that you are contributing".
He added: "At that particular point . . . it could be a year, it could be two years, after that, then we will consider you a resident of the UK and be happy to pay you benefits."
Sources close to Mr Duncan Smith stressed that he was merely expressing an aspiration for the future, rather than spelling out a policy.