The House of Lords reform bill is published amid threats of a rebellion from Conservative MPs worried that the supremacy of the Commons could be threatened.

House of Lords (Getty)

The bill has been published by the Cabinet Office after its first formal reading in the House of Commons on Wednesday.

The legislation, which would introduce an 80 per cent elected upper house and reduce membership by 350 to 450 Lords, has proven controversial with both Conservative and Labour backbenchers.

Lord Peter Hennessy has called it the "Bermuda Triangle of political reform".

The bill, which was approved by the cabinet on Tuesday, is the remaining centrepiece of Liberal Democrat constitutional reform plans. Following last year's defeat on voting reform, Deputy Prime Minister Nick Clegg is hoping to drive it through by the spring.

Mr Clegg is, however, facing resistance from within the coalition as well as from the opposition.

While Labour leader Ed Miliband has announced his party will back the reforms, it will join with Conservative rebels in pushing for longer to debate the legislation by voting down the motion which sets out the bill's passage through parliament.

If Labour and the Tory rebels get their way, and Mr Clegg's proposed timetable is defeated, four to five weeks of extra debate will be added to proceedings in August.

Mr Miliband, who argues the bill contains a number of "flaws", said he wanted the bill to "be properly discussed in both houses".

One of the major flaws for Labour is the lack of a national referendum on the subject. The party is expected to table an amendment demanding one.

Prime Minister David Cameron dismissed Labour's stance as "hopeless".

During today's Prime Minister's Questions Mr Cameron said that he believed there was a majority for Lords reform, but that supporters needed to stand up and back it to get the proposals through.

Mr Cameron said: "The truth of the matter is this: there are opponents of Lords reform in every party - the Conservative Party, the Labour Party and in the Liberal Democrat Party in the Lords.

"But there is a majority in the Commons for a mainly-elected House of Lords, and I believe there is a majority for that in the country.

"But if those who support Lords reform don't get out there and back it, it won't happen. That is the crucial point."

Although Conservatives will be "whipped" to support the legislation, ministerial aide Conor Burns has already announced he is prepared to sacrifice his job to vote against the timetable.

Mr Burns, the parliamentary private secretary to Northern Ireland Secretary Owen Paterson, told BBC Radio 4's Today programme: "This is major constitutional change. Major constitutional change is not usually guillotined in debate."

"If we are going to have this debate, we need to have it at length and in full and we should have it in committee on the floor of the House of Commons and we should take as much time as is necessary to do that.

"If I lose my job for something that was a mainstream view within the Conservative party in the last parliament, which serving cabinet ministers held as their view, so be it."

A revolt amongst rebel Tory backbenchers appears likely.

What is in the bill?

* The proposals in their current form would complete the removal of hereditary peers from the second chamber.

* The first elected members would be introduced at each of the next three general elections - in groups of 120.

* Voters would be able to elect members of the reformed House of Lords for the first time in May 2015, with the process scheduled for completion by 2025.

* Once elected, members would serve for a single 15-year term.

* Existing peers would be phased out as elected members are brought in.

* Instead of the £60,000 salary for members of the upper house originally proposed, they will receive £300 for each day they attend, up to a maximum of £45,000 per year. Unlike the current attendance allowance paid to peers, this payment will be taxed.

* Once the reforms are completed the real terms cost of parliament is anticipated to be broadly the same as it is now.

* The bill insists the reforms will maintain the primacy of the House of Commons within parliament.

Critics warn that the added clout of democratic legitimacy would place the primacy of the main house under threat.

The bill will have its second reading in the Commons, followed by the vote on the timetable motion, before parliament breaks for the summer on 17 July.

The government's response to the joint committee's report can be read here.