70 Conservative MPs intend to rebel against Government's Lords reform motion The MPs, who include senior Conservative select committee chairs, have written to their colleagues advising them that they will vote against the Government on a timetable (or programme motion) for the bill. This is despite a warning by Nick Clegg's most senior aide in The Independent last week that such a rebellion would have "broader consequences" for the Coalition. Losing the programme motion would leave the legislation vulnerable to being "talked out" by opponents and leave the Government in what the Lib Dem source said would be "uncharted territory." The Lib Dems are understood to be prepared to vote against Tory plans to cut the number of MPs at the next election - a vote which would make it harder for David Cameron to win an outright majority in 2015. Mr Cameron is understood to have spent the weekend phoning round Tory MPs in an attempt to get them to vote with the Government. The Prime Minister's official spokesman said this morning: "No-one should be in any doubt his position." But in a sign that neither threats from the Lib Dems or appeals from Downing Street are working the 70 MPs have signed a joint letter telling colleagues suggesting they intend to defy Mr Cameron in tomorrow's vote. The list includes Tory grandees such as Bernard Jenkin, Malcolm Rifkind, James Arbuthnot, Graham Stewart and John Whittingdale, all committee chairmen. It also includes prominent new members elected in 2010 including Nadhim Zahawi, Rory Stewart, Jesse Norman, and George Eustice. It reads: "Dear Colleagues. We come from all sides of the Conservative Party, and are writing as reformers to express our serious concern at the current proposals to create an elected House of Lords. The Lords Bill is a measure of profound constitutional significance... It threatens to pile a constitutional crisis on top of an economic crisis. Specifically what is now proposed will undermine the primacy of the Commons, with competing chambers which will lead to legislative gridlock. It will create hundreds of unaccountable new elected politicians at a time when we as a party are committed to reducing the cost of politics and it will produce a chamber which is less expert, less diverse and significantly more expensive than the present one. The commitments in our 2010 election manifesto and in the Programme for government - to seek consensus and to bring forward proposals - have been fulfilled. We hope you will support us in giving this Bill the full and unrestricted scrutiny it deserves. The legislation, central to the Lib Dems' agenda in the coalition, would introduce an 80 per cent elected Upper House and slim down membership from 800 to 450. It would finally complete the removal of hereditary peers and replace them with members elected under a form of proportional representation for a single 15-year term. Another 90 members will be appointed by a statutory Appointments Commission on a non-party basis and there will also be 12 Church of England bishops - down from 26 church representatives. Liberal Democrat Foreign Office Minister Jeremy Browne said Tories "need to remember they didn't win the general election either" and that each side had an "obligation" to stick to the deal. But Baroness Boothroyd of Sandwell, the former Speaker of the House of Commons, urged rebels to ignore party political "blackmailing" and vote down the Bill. "I have been in Parliament nearly 40 years," Lady Boothroyd told the BBC Radio 4 Today programme. I have never witnessed such a reckless attempt to change the British constitution, and to do it on such spurious grounds, quite frankly. What they are seeking to do is limit debate on this major constitutional issue. I believe it is an outrage and I think it is an abuse of Parliament. Lady Boothroyd insisted that she was in favour of reform, but to have two elected chambers could lead to clashes over issues such as war. "This Bill has not been thought out," she said. "I say to the people who are defying the Whip "Good luck to you, you are doing the right thing by your constituents, by your country and by Parliament." Forget about the blackmailing of the party politics that is going on at the current time. Mark Harper, the Constitutional Reform Minister, defended the Government's attempt to limit the time for debate - the measure that faces defeat in the vote tomorrow. "I don't think we should talk about it for ever," he told Today. There are other important issues that Parliament should determine. He insisted that the plans had been extensively scrutinised, and the wider issue had been debated for more than 100 years. "I think colleagues will support it when they look at these proposals," he said. They are well thought through, they have been scrutinised by a committee of both Houses. Mr Cameron knows that defeat could trigger a backlash from Liberal Democrats, who have threatened to vote against changes to MPs" constituency boundaries that could favour the Tories at the next election.