Today’s news that David Cameron has promised reselection to every sitting Tory MP who wants it is a sign of how important fairer boundaries are to the current leadership.

The reason is obvious enough: Labour currently enjoy a significant structural advantage in the distribution of their vote, and if seats were equally sized it would not only produce fairer results but, by happy coincidence, much more comfortable Conservative MPs.

Yet this measure, along with a couple of others, as set up something of a hue and cry amongst parts of the British left, who claim the Tories are staging a quiet, constitutional coup d’etat.

The New Statesman accuses them of “rewriting the constitution to create a one-party state”, whilst in The Guardian Owen Jones implores “decent Tories” to stop the Government pursuing boundary and franchise reform – measures which, in his words, “imperil centuries of progress”.

Regardless of the merits and demerits of individual proposals – and they all seem perfectly defensible from where I’m standing, although they would – it should be born in mind that the red team are just as culpable as the blue when it comes to constitutional tinkering.

I remember when advocates of proportional representation were crowing that it would unlock Britain’s “progressive majority” and lock the Tories out of power forever.

(Many of those trying now to introduce PR to Parliament via a Senate are similarly motivated. The idea that PR-minded parties – or indeed, any party better represented in a Senate than in the Commons – would long cleave to the notion that the Commons is the superior chamber is for the birds.)

Prior to that, we had lopsided devolution settlements designed to lock down Labour heartlands and create political cultures free of the “tax” bit of “tax and spend”.

It is perhaps natural that the authors of such schemes should, upon seeing the boot transferred to the other foot, flinch in anticipation of a righteous kicking.

Nor is there any reason to believe the left have foresworn further constitutional meddling, if this despairing piece by Polly Toynbee is anything to go by. She writes:

“Labour will only win when its members decide it’s worth compromising to oust the Tories from power, as they finally did after their fourth miserable defeat in 1992. Then they can have electoral reform, and then they can split if they wish.”

Translation: now that the current electoral system no longer fits us, we shall abolish it and hope for gentler treatment in the new order of things.

There is a principled case to be made for PR (as there is for the Government’s tweaks to the current system). Yet enthusiasm for it only really breaks out in the major parties of British politics as a counsel of despair.

Only when winning big looks impossible does the prospect of winning small really appeal.

If Labour stormed back into office with a clear vision and a charismatic leader, the idea of voluntarily splitting their winnings with a greatly-inflated caucus of ‘Others’ would be no more to the liking of the next Tony Blair than the last one, who abandoned Paddy Ashdown’s Liberal Democrats the moment he could go it alone.

To uphold the constitution then, the Conservatives need to prevent a suicidal Opposition from lurching over the line and taking the voting system with it.

That means winning comfortably until Labour – or whatever follows Labour – is in a fit state to win properly. And that needs boundary reform.