Maybe we should have expected as much. It was always going to be difficult to keep Ken on board while he was running for Mayor of London. His stated reasons for changing sides are so irrational that he can't really expect us to take them seriously.
Lord Jenkins has put forward two moderate changes to the system to deal with its most obvious defects - preferential (1,2,3) voting to eliminate the need for tactical voting, and a small number of top-up seats to deal with the problem of wasted votes without increasing the likelihood of coalition government.
Ken argues that a referendum may be lost because Jenkins does not offer genuinely proportional representation. But we all know the reverse is true. A pure PR scheme would stand no chance at all, because most people simply do not want permanent coalition.
Ken argues that the preferential Alternative Vote can be even less proportional than first-past-the-post. Well, occasionally, it can. But Jenkins isn't proposing AV. It may be known as AV Plus, but it is really a top-up system and the top-up seats compensate for the disproportionality of AV. The faults of AV are thus largely irrelevant.
The aim is not to achieve perfect proportionality. It is to ensure that votes count and the Surrey Labour or the Glasgow Tory will at last be represented. It is the only chance of getting reform.
So, Ken, take a lesson from Dick Whittington. Think again.