Media playback is unsupported on your device Media caption David Cameron: "Is it in our interests to reform the European Union? Yes, it is"

The Conservatives have published a parliamentary bill setting terms for a referendum on whether the UK should leave the European Union, in the hope of reassuring the party's MPs.

Many Tories are unhappy plans for an "in-out" vote were not mentioned in the Queen's Speech, and will try to amend it in a Commons debate on Wednesday.

But the draft bill says it "must be held" before the end of 2017.

David Cameron's spokesman said this offered a "clear route" towards change.

The draft bill, containing six clauses, would - if passed into law - set out how the Conservatives would deliver their promised referendum if they win the next election, due in 2015.

'Regret'

It would mean UK voters being asked the question: "Do you think that the United Kingdom should remain a member of the European Union?"

This would follow attempts by a Conservative government to renegotiate terms of the country's relationship with Brussels.

The fact the draft bill was not mentioned in last week's Queen's Speech, which lays out the government's plans for the next year, infuriated many Tory MPs who want the pledge firmed up or accelerated.

The publishing of a draft bill looks like an exercise in what Mrs Thatcher used to call 'followership not leadership'.

In a debate on the Queen's Speech this Wednesday, they will propose an amendment, expressing "regret" at the failure to include it in the government's plans.

There is little chance of this succeeding, as the Liberal Democrats, Labour and pro-European Tories oppose it, but a significant vote in favour would be an embarrassment for the prime minister.

Around 100 Conservative backbenchers and ministerial aides are expected to back the amendment or abstain, but the party leadership is hoping to reduce this number by publishing the draft bill.

Foreign Secretary William Hague told the BBC that publishing the draft bill was a "demonstration of our commitment to a referendum".

And Downing Street said: "The prime minister has set out a very clear route for this country to take and nothing that has happened has changed that path."

Analysis David Cameron's move is designed to do two things. First, to placate Conservatives on his own side who are planning to express their displeasure at him for not going further on a referendum. Second, to force the Liberal Democrats - and more importantly Labour - to come out and declare where they stand on a vote. On the first it does not appear to have worked. Tory MP John Baron has led the calls for more than just a prime ministerial pledge to hold a vote by 2017 - he wants a law. But he is not impressed. He said publishing a draft bill was "not good enough", then urged Tory rebels to stick to their plan and vote against the Queen's Speech on Wednesday. David Cameron does have a longer-term aim here - the second point. This proposal may have little chance of becoming law but it could force Ed Miliband to take a long hard look at his policy on a referendum. Labour is currently against a pledge to back one now, saying it is more than four years off. But the prospect of being the party which comes out against a national vote, against the first expression of national will on Europe in almost 40 years, is something that some in the opposition believe would be deeply unpopular.

The spokesman dismissed any comparisons between Mr Cameron and former Prime Minister Sir John Major, whose government was damaged by ongoing rows about Europe during the 1990s.

The draft legislation is being published by the Conservatives so that it can be brought to the Commons for debate by one of the party's backbench MPs in the form of a private member's bill, rather than one sponsored by the government.

The ballot to choose who can bring forward private members' bills will be held on Thursday and, although they have little chance of becoming law, there is non-government parliamentary time available for them to be debated.

BBC political editor Nick Robinson said the Conservatives' strategy was aimed at persuading the public they would only get an EU referendum if they vote for them at the next election and contrast this with Labour and Liberal Democrat opposition.

On Monday, Mr Cameron - who is on a trip to the US - said his approach was in the "national interest" and holding a referendum now would provide a "false choice" between the status quo and an immediate exit.

Nevertheless, two senior cabinet ministers - Defence Secretary Philip Hammond and Education Secretary Michael Gove - have said they would vote to quit the EU if a poll was held straight away.

'Bogged down'

Conservative chairman Grant Shapps told BBC Radio 4's The World at One that the draft bill had been in preparation for several months and the timing of its publication had nothing to do with Wednesday's vote - in which MPs were "entitled" to express their views.

But Tory MP Philip Hollobone told the same programme that No 10 had been "in chaos" over the past week on the issue and it should have published the draft bill at the time of last week's Queen's Speech.

PRIVATE MEMBERS' BILLS MPs put names into a ballot

Normally the first seven drawn are given a day's debate for their bill

Most private members' bills - lacking government support - do not become law

There have to be at least 100 MPs backing a bill to ensure it clears the first few hurdles

But one with the backing of Tory ministers but not Lib Dems would be likely to fail to get a majority unless a decent chunk of Labour MPs back it

And Eurosceptic Tory MP John Baron, one of the key movers behind the Queen's Speech amendment, said the PM should have the "courage" to support it and "force Labour and the Liberals to decide" their position on the EU.

More pro-European Conservatives have said there must be an orderly process leading up to any vote over the UK's future in the EU.

Former Justice Secretary Ken Clarke urged his colleagues to "move on" from the current wrangling and warned that leaving the EU would be "catastrophic" for the UK's economic prospects and global standing.

Labour says committing to hold a referendum in four years' time is not the "right choice" for the country and internal Tory "machinations" are causing uncertainty at a time when securing economic recovery should be the government's priority.

Media playback is unsupported on your device Media caption John Baron MP: "That is a ploy that could well fail"

"Our agenda is reform and change within Europe, not exit from the European Union," said shadow foreign secretary Douglas Alexander.

The Lib Dems said the government had already legislated to seek public approval before any further powers were handed to Brussels, and accused their coalition partners of "navel-gazing" over Europe.

The UK Independence Party - which campaigns for a UK exit - has raised the possibility of Conservative and Labour candidates who favour withdrawal standing under a joint banner with UKIP at the next election.

Leader Nigel Farage described the proposed draft bill as "nothing more than gesture politics".