A senior Liberal Democrat peer today warned Conservatives that they must back coalition plans to reform the House of Lords - despite a threatened revolt by Tory backbenchers.
Conservative MPs were reported to have lined up to condemn the proposals - set to form the centrepiece of next month's Queen's Speech - at a "stormy" meeting last night of the party's backbench 1922 Committee.
A number of ministerial aides were reported to have indicated they would rather resign than support legislation for a largely - or wholly -elected upper chamber.
However, Lib Dem peer Lord Oakeshott insisted today that the plan was part of the coalition agreement and should be supported by MPs of both parties.
"Our vast unelected House of Lords is overstuffed with complacent dinosaurs," he said.
"Electing both Houses of Parliament is a simple democratic principle, it's in all three major parties' general manifestos and the coalition agreement.
"So all coalition MPs should back it - and Labour mustn't drag their feet on this long overdue reform."
The issue of Lords reform threatens to stretch coalition unity to breaking point in the coming months.
Deputy Prime Minister Nick Clegg has insisted it is an essential part of the coalition's constitutional reform programme.
Lord Oakeshott has previously warned that Lib Dem peers could wreck Tory plans to cut the number of MPs if it does not go through.
On Thursday Clegg denied there was a link between the two proposals and said Lord Oakeshott did not speak for the Lib Dems as a party, but he warned his Tory colleagues that he expected them to support the creation of an elected Lords.
"I expect the same civility and consistency from all sides in this coalition to press forward with all these issues whether people like them or not," he said.
On the Conservative side, many backbenchers - already frustrated at the Lib Dems' influence within the coalition - are adamant they are not prepared to support measures that could, they believe, upset the whole balance of the constitution.
Many Tory MPs are pointing to the Coalition Agreement, which states that the government is committed to "bring forward proposals" to introduce an elected House of Lords, but does not require them to actually vote in favour of it.
Similarly the agreement committed Lib Dems to "bring forward" plans to cut the size of the House of Commons but does not commit them to voting in favour of it.
Downing Street said David Cameron remained committed to reform of the House of Lords.
"Both the prime minister and the deputy prime minister are committed to Lords reform," a No 10 spokeswoman said.
She added that all members of the government would be expected to support the legislation when it comes to Parliament.
"If it is government policy, one expects the government to support it," she said.
Clegg also faces a battle with Labour over his Lords reform bill. While the Opposition support plans to create an elected second chamber, it has decided to push for a referendum on the issue.
Ed Miliband said that while he supported reform, there should be a referendum given that it was a "major constitutional change".
"I think the best way of making sure that House of Lords reform happens is by giving people a say," he said.
"We’ll obviously see what the committee that has been set up to look at this says on Monday but Labour’s view – which we expressed in our manifesto – is we want a democratically elected second chamber, we wanted a referendum to make that decision and I hope the Government will listen to what people are saying and hopefully what Parliament will be saying."