In each case, a small group of independent-minded peers was willing to listen to, and be persuaded by, arguments that when such subjects were presented in the classroom, or examined in the broadcast media, this must be done evenhandedly. Such was the strength of opinion in the Lords that, on both occasions, amendments made there were allowed to remain when the bills returned to the Commons. An upper house, filled from party lists of professional politicians, would be no more receptive to any of these arguments than the House of Commons — where almost all the votes are strictly whipped and where defying the whip is an act of career-changing rebellion. 

The willingness of members of the House of Lords to judge arguments on their merits, and to amend legislation accordingly, stems not just from the limited discipline which can be imposed upon them. It derives, in large measure, from the fact that many peers are appointed after reaching the summit of their professions. They therefore have an expertise which full-time MPs might have achieved, had they not switched careers to enter the Commons. It is not the same to be a potential expert, who decided instead to become a full-time politician, as it is to be an actual expert, who entered the Lords after reaching the top of the medical profession, the armed forces, business, the Church or the arts. 

Young full-time politicians may well be able to see the strength of an argument for amending a bill; but their careers are still in front of them and only a minority will put ambition aside to vote for an amendment of which the front bench disapproves. Once most (or all) members of the upper house have to win selection and fight elections, eminent greybeards will be marginalised, if not excluded entirely, by a younger generation of machine politicians.

Few deny that the calibre of debate in the House of Lords is higher than that in the Commons. This will cease with the exit of the experts. No one, when challenged, can point to any inadequacy in the way the House of Lords fulfils its role as a subordinate chamber dedicated to the revision, refinement and improvement of detailed legislation. The only objection which is ever made comes in the form of a mantra: that it is "not acceptable in the 21st century" for any part of the legislature to be unelected.

In reality — and irrespective of all the ways in which an elected upper house would undermine the lower one — the removal from our system of those who have reached the top of their respective careers, and the substitution of people who have barely begun to do so, will spell the end of the House of Lords as a place where laws are fine-tuned and enhanced. A second chamber of elected politicians will be no better equipped for this task than existing MPs. Electing the Lords is a piece of constitutional vandalism. It deserves the same dismal fate as that other Liberal Democrat obsession, the Alternative Vote. That is why a referendum is essential.