If there’s one area where defenders and critics of the House of Lords appear to be finding some common ground, it’s that the upper house has got too big.

There is a case to be made that, in a chamber intended to be staffed by a diverse range of people with expertise and experience rather than full-time, professional representatives, this isn’t necessarily a flaw.

After all, a core of active peers supplemented by a broader pool of lords who only attend to bring their expertise to bear on certain subjects – and aren’t paid when they don’t attend – isn’t an inherently illogical system, for all that it diverges from the American model of bicameralism.

But if the consensus is forming that the House of Lords needs to shrink, that’s going to be more challenging than it might first appear.

One of the main reasons for the inflation of the upper house is that, as there is currently no sunset clause in an elevation to the peerage, the only way for a governing party to strengthen its position on the red benches is to appoint even more new peers.

This shouldn’t be necessary if the Lords were true to its intended function as a relatively non-partisan chamber for scrutiny and recommendation.

But activists for an elected chamber are deliberately trying to subvert this convention in order to undermine the upper house – a point explicitly made by Dr Mark Pack, a Liberal Democrat commentator:

“More Liberal Democrat peers willing to vote down government business certainly threatens the current way the Lords work. While the deeply conservative elements of other parties, and indeed Parliamentary staff, look at this with horror, Liberal Democrats (and anyone wanting Lords reform) should welcome this…”

This highlights the challenge implicit in the initially simple-seeming reform of shrinking the House of Lords.

If the Government introduce a mechanism to give peers anything resembling terms, and to fix the partisan balance so that it at least approximates the Commons, they’re playing straight into the hands of those who want an elected senate, the establishment of which is the logical (to a given value of logical) conclusion of such reforms.

But if the Lords is to continue to play its current role as a place of expert scrutiny and recommendation, there will need to be mechanisms in place to prevent it being hijacked by party partisans.

This would almost certainly entail a sharp reduction in the number of party political appointments – and a commensurate loss of valuable patronage for party leaders.

It also risks making the upper house a less honest place, as the political composition of the chamber and biases of its members – and such biases will always exist – will become harder to spot.

Those of us who have actually sat down and covered debates in both chambers often have a deeper appreciation of the merits of the Lords than some of its critics. Whatever your opinion on it, its transformation into an elected or proto-elected chamber is too important a change to be enacted in a bout of absent-mindedness.

If there is one lesson to take from the Blair years, it must be that rushed constitutional changes are almost impossible to be rid of and store up trouble for the future. The Government must not allow itself to be bounced into rushing reform.