There are few better illustrations of the need for institutional political reform than the constantly spiralling size of the House of Lords. The scale of ermine-clad inflation at Westminster is now genuinely shocking. Today the Lords has nearly 850 “potentially eligible” voting members, an increase of 112 since 2010, up by a third since the removal of most hereditaries in 1999. It is hard to see the current system as anything other than a form of political corruption and its expansion as evidence of a system in collective denial.

Yet without moves to control it, things will get more absurd. The UCL constitution unit, in a study published on Tuesday, says that if the rate of peerage creation continues on the basis of the coalition’s formula, there will be between 1,354 and 2,207 peers by 2025, an incredible total. Even on the lower figure, there would be 2,000 legislators at Westminster, a ridiculous and indefensible number.

The Commons itself is very large. But the size of the Lords is the real problem. There is no other bicameral legislature anywhere in the world in which the upper house is larger than the lower house. The case for change is overwhelming – morally, democratically and on every other ground.

All the political parties are expected to go into the general election with proposals for Lords reform. Yet such reforms will take time – and earlier efforts have repeatedly been postponed or frustrated. In the meantime, governments will go on appointing more new peers for party advantage. Fully 75% of David Cameron’s 187 Lords appointments have been on the Tory or Lib Dem benches, for example. But an Ed Miliband government would undoubtedly be under pressure to redress that advantage under Labour – and there are plenty of retiring MPs who are fully expecting to be seamlessly translated to the Lords in May anyway.

As the constitution unit says in its report, Enough Is Enough, the House of Lords is too important to be left to prime ministerial whim. The existing system has failed. So let’s bin it. It would be a scandal if Mr Cameron, Mr Miliband or any other future prime minister were to continue this way. The report’s authors call for a pre-election agreement to place a cap on overall numbers at around 550 and to agree a new formula – based on election vote share – under which the size of the upper house will be managed downwards over coming parliaments.

Such a pact and pledges would be a good temporary fix to peer inflation; let’s hear party commitments to this effect soon. But the big need after May is to create a much smaller, democratic and federally based second chamber, perhaps not in London, as part of the wider and urgent renegotiation of the UK’s whole constitutional framework.