House of Lords reform: riven coalition prepares for testing bill House of Lords reform is one of the coalition government's more divisve policy areas. Ministers are bracing themselves for potential coalition clash with the announcement of fresh safeguards on an elected second chamber, designed to mollify an imminent Conservative rebellion. The government will unveil its House of Lords reform bill on Wednesday and set out the future of parliament's second chamber. The reforms have been driven by the Liberal Democrats, and have become the focus of disgruntlement among Tory backbenchers. Ministers are expected to respond to a joint committee report on Lords reform by reasserting the supremacy of the Commons over a mainly elected second chamber and highlighting new government legal advice that the existing Parliament Act will prevail in the event of a dispute between the two houses. The Parliament Act prevents the Lords rejecting the same legislation twice. It has been argued that the Parliament Act would no longer apply once the second chamber is elected, or at least the powers of the Commons would be challenged by a newly assertive elected second chamber. As many as 100 Tory MPs, some eager to pick a fight with their Lib Dem colleagues, have told their chief whip they could rebel over Lords reform - including a small number of parliamentary aides. The threat of an elected second chamber supplanting the powers of MPs, so creating constitutional deadlock, has been their chief objection. The bulk of the changes to be announced this week by the Cabinet Office minister Mark Harper and the deputy prime minister, Nick Clegg, are designed to allay these fears. The new bill will also use European parliament boundaries so as to make clear that the new elected peers are not duplicating or usurping the constituency work of MPs. The elections will be by single transferable vote, but the bill will also stress an open-list proportional system for the elections, ensuring that closed party lists selected by party machines cannot be presented to the electorate. This should ensure independently minded candidates will have a chance of winning. The Conservative deputy chairman, Michael Fallon, speaking on Sky News's Murnaghan show, said "huge safeguards" had been inserted into the bill to meet the objections of his backbenchers. Ministers have not been eager to set out in the bill the precise legal relationship, and conventions between the two houses since this would then make the relationship subject to judicial intervention. On Tuesday Danny Alexander, the Lib Dem chief secretary to the Treasury, will make a speech on the case for reform to the Electoral Reform Society. Alexander will argue that it is possible to restore the economy to health, and simultaneously continue with political reform. Opponents of Lords reform have argued constitutional change is an irrelevance or a distraction at a time when the priority should be addressing the lack of growth in the UK. Alexander is seen by Lib Dem officials as totally committed to improving the economy, but who also argues the case for democratic modernisation. He will also point to elections for police comisisoners, which are going ahead this year. Without Lords reform, they will be asked to handle crime legislation passed by unelected peers. Clegg has been assured that David Cameron, the prime minister, will back him on the reforms. In a sign that the Tory hierarchy knows the political importance of the reform to the Liberal Democrats, Fallon said: "This is a coalition policy, it will be a coalition bill, it's going to the coalition cabinet this week, so it's a coalition piece of legislation that has the full force of the coalition behind it." Cameron and Clegg have not bowed to demands to hold a referendum on the reforms - a key Labour policy plank at the last general election. Fallon said he could think of better things to spend £100m on, and was not necessary since the bill will not detract from the powers of the Commons. In an interview with the Guardian last week, Miliband refused to set out how his party would respond on Lords reform until it has seen the legislation but it is understood that he is pro-reform. Lib Dem peers well disposed to Labour see the issue as a key test of whether the party is willing to co-operate or instead put opportunistic damage to the coalition ahead of everything. It has the opportunity to form an alliance with Tory rebels either to reject a business motion timetabling the debate, or to vote with the Tories to demand a post-legislitive referendum. The business motion is not expected to be debated until mid-July, just before parliament rises,. If parliament rejects the business motion, there would be no timetable, or guillotine, for the Commons debate on Lords reform. Clegg and Cameron will have the summer to decide whether to press ahead. They could retreat if they were sure that interminable debates on the issue of Lords reform would gum up the Commons for the rest of the parliament, so endangering other legislation.