An unedifying game of political poker is being played out over Nick Clegg's proposals to reform the House of Lords. Until yesterday, the Conservative and Labour parties were playing their cards in public. As a result of the interview in The Independent with Mr Clegg's outgoing senior aide, Richard Reeves, the Liberal Democrats have joined the table too. Mr Reeves warned Conservative MPs that they would not get their constituency boundary changes, worth about 20 seats to David Cameron's party, if they blocked Lords reform.

Next week MPs will vote on Mr Clegg's proposals and, equally importantly, on the amount of parliamentary time available for scrutiny. An innocent spectator of the poker game on the eve of this pivotal moment would be surprised to discover that all three players went into the last election pledged to reform the Lords.

Such purity of aspiration at the election is replaced now with crude, expedient calculation. Mr Cameron supports the reforms not because he is keen on them, but in order to keep the Coalition together – and more specifically to ensure that the Liberal Democrats do indeed back the boundary changes that will benefit his party. Some Conservative MPs appear ready to oppose the reforms on the grounds that they are furious with the Liberal Democrats for various reasons that have no connection with the House of Lords.

Meanwhile, the Labour leadership has decided to vote for the reforms, but to oppose the limited amount of parliamentary time available to scrutinise them, an act of contrivance that allows Ed Miliband and others to affect support while almost certainly killing off the chance of elections for a reformed second chamber taking place on schedule in 2015.

Now the Liberal Democrats play their card in public. Mr Reeves's threat to the Conservatives is a potent one. Mr Cameron might need those additional 20 or so seats in a close election.

All of them should step back and focus on the issue at stake. That includes the Liberal Democrats. While understandably worried at the prospect of a revolt among Conservative MPs, they undermine their justified criticisms of the other two parties when they openly link an entirely separate reform, the boundary review, with their plans for Lords reform. The review is one to which they have given their support and should therefore continue to do so instead of threatening to withdraw it, not on the merits of the case, but as a threat to Conservative MPs. Even as a tactic it is unlikely to work, as rebel Tories will regard the warning as a provocation rather than as an inducement to support Mr Clegg's proposals.

Similarly, the two bigger parties should place to one side their parochial multi-layered calculations and focus on the opportunity to reform the non-elected second chamber. The poker game is a diversion from what should be a rare act of consensual politics given that all three parties are pledged to reform the Lords.

MPs will be debating Mr Clegg's proposals on Monday and Tuesday. One way or another they have been debating House of Lords reform for more than 100 years. More specifically, since 1997 there have been endless attempts at reform and committees set up to come up with proposals. Mr Clegg has worked assiduously and consulted widely to ensure that some of the previous issues which caused deadlock have been addressed.

So MPs and their aides can continue playing poker. Or they can ask a simple question: is it justified in a modern democracy for part of the legislature to be non-elected and unaccountable? Most MPs know the answer is no and should therefore support the proposals next week and also the legislative timetable that allows enough time to debate the issue – one which has been scrutinised more intensely than any other in recent times.