The joint committee on House of Lords reform will publish its long-awaited report today, a document which will set the tone for what's becoming an increasingly factious coalition issue.
Up to 100 Tory MPs - including some ministerial aides and even Cabinet ministers - are thought to be deeply hostile to Nick Clegg's plans for reforming the Lords.
The draft Bill published by the government would see a gradual change from the largely appointed Lords to a largely elected chamber. Every five years about a quarter of the appointed Lords would be removed and replaced with elected members, who would serve a long fifteen-year term. They wouldn't be allowed to stand again.
These new peers would have super-constituencies, and there would be about 300 of them. By 2030 the upper chamber would consist of 80% elected peers, and 20% would still be appointed. The Church of England Bishops would keep twelve of their seats.
The biggest complaint is that the government's plan for the Lords fails to enshrine the supremacy of the House of Commons, even though ministers insist this is exactly what they are doing. Although the Committee's report is under a strict curfew until 10 o'clock this morning they are likely to challenge the government's plan to retain the Parliament Act - the piece of law which allows the Commons to eventually over-ride the Lords on any piece of legislation the unelected house seeks to block.
Ministers believe there is no need to change this Act - which has existed in some form for 101 years - arguing that it would perform the job perfectly well even if the Lords were elected. The committee members have repeatedly questioned how a piece of law designed to clamp down on the powers of an unelected chamber could work when dealing with an elected one.
Another recommendation which could be in the report is a call for a national referendum before the changes to the Lords can come into force. This is expected in part because of a leak of an early draft of the report before Easter, which was said to contain the referendum demand.
Labour have put their weight behind this idea, saying such constitutional change shouldn't happen without the public being consulted. The coalition have dismissed this, pointing out that all three main parties went into the 2010 general election calling for at least part of the Lords to be elected.
Tory Ministers are said to be openly questioning the merits of Lords reform around the Cabinet table. Sunday papers reported that heavyweights like Michael Gove and Philip Hammond are uneasy. Further down the food chain there are Tory Parliamentary Private Secretaries - ministerial assistants who don't get paid for their efforts but must always vote for the government or resign - have been openly critical.
Tory MP Conor Burns - who is PPS to the Northern Ireland Secretary - was open in his dissent on Friday, telling BBC Radio 4: "My view hasn’t changed from the view I expressed in the House of Commons to the Deputy Prime Minister that I am in favour, broadly, of the status quo."
Burns is one of dozens of Tory MPs who believe a vote in the Commons on this matter should be free, and not whipped by the government. Previous Lords reform votes have always been free, and Burns told Radio 4: "If the Deputy Prime Minister is right, that there is a majority in the House of Commons, across Parliament, across parties, then it will go through."
Burns' statement suggests there is little that ministers can do to appease some Tories, even if they agree to further concessions. These were hinted at in reports on Sunday, suggesting Nick Clegg might agree to the new Lords having 450 members, rather than the 300 he originally envisaged.
There is a gamble for David Cameron in all of this. Abandon Lords reform and the Lib Dems could easily threaten to block other bits of the coalition agreement, including the Tories' cherished plan to reduce the number of MPs by 50 and shake up the boundaries to lessen Labour's inbuilt electoral majority. Lib Dem MP Lord Oakeshott recently made this threat on the Sunday Politics programme on BBC One.
Nick Clegg was at great pains to deny this would happen on Friday, when the coaliton tensions about this rose to the surface. But what else have the Lib Dems really got on the Tories as leveage? Some people in Nick Clegg's party are starting to think that their poll numbers are just wrong. They continue to languish in single digits in national opinion polls - and have by all accounts been taken over by UKIP.
But every time there is a by-election for either a council seat or for Parliament, they actually do much better than the polls suggest. The notion that the Lib Dems are stuck in the coalition because to trigger a general election would cause wipeout is starting to look quite shaky.
With the AV referendum out of the way and many of the things that the Lib Dems wanted already passed into law, the reasons for them to stay in coalition -other than the threat of wipeout at the ballot box - are fewer in number than a year ago.
But on the other hand if David Cameron presses ahead with Lords reform he risks a mutiny among his own backbenchers, and even if he can control that, could find that the Lords will get so aggravated that they won't just start delaying the law to abolish them, they could start being difficult over every other piece of legislation the government sends their way.
All this for a reform which the public clearly doesn't care about whatsoever. Sure, if you ask them whether the Lords should be elected they mostly agree that it should. But how many letters do MPs actually get from people urging them to do something about it? Very few indeed. The third and final risk for Cameron is that he is seen to be distracted by Westminster intrigue about the Lords, at at time when the public are severely underwhelmed by his management of the economy and the NHS.
It's those two things, after all, that most analysts expect to be the biggest issues at the next general election. Not who sits on the red benches in Parliament.