After all, there is not anything quite like the Jenkins system anywhere else in the world.
True, it is a variant of the Additional Member System used in Germany since 1945, and introduced more recently in Italy and New Zealand. But none of these combine the system with the alternative vote. And the 15- 20 per cent of MPs to be elected as "additional" members contrasts sharply with the 50 per cent elected that way, for example, in Germany.
So the relevance of any arguments, from either camp, about what have been the consequences of proportional representation elsewhere will need close scrutiny.
Indeed, it would be a mistake to regard Jenkins' proposals as a proportional system at all. After all, it would still have given Tony Blair a thumping majority in 1997, with just 44 per cent of the vote.
We cannot assume that coalition government would be an inevitable consequence of the introduction of this system at all.
Of the last five elections, only in 1992 would the winner have been different. John Major would have been struggling to remain in office, although Labour and the Liberal Democrats combined would not have had a majority either. But Mrs Thatcher would still have won her three elections in a row, albeit with much smaller majorities.
In any event, the current system's recent record in producing strong governments with safe overall majorities has not been all that impressive. Of the last seven elections since February 1974, it has delivered weak governments on no less than three occasions - twice in 1974 and again in 1992. Jenkins seems unlikely to have done any worse.
Only before 1974 would the system have made a big difference. All of the seven elections between 1950 and October 1974 produced a winner. But under Jenkins, only Labour's 1966 victory would definitely have been repeated, with perhaps the Conservatives possibly just squeezing home in 1959.
The reason is simple. In the Fifties and Sixties, elections were closely fought affairs, with neither of the two big parties pulling far ahead of the other in votes. While first-past-the-post may sometimes produce a majority in such circumstances, Jenkins hardly ever would.
Then there is the other favourite argument of the anti-reformers - that proportional representation would destroy the link between the individual MP and his or her constituents.
Under Jenkins, at least 555 MPs, and maybe as many as 619, would still be the only MP for their constituency. No MP would be serving an area greater than a county or city.
So, favouring the constituency link no longer looks like a good enough reason to oppose reform.
However, Jenkins has also robbed the pro-reform lobby of some of its best tunes. That lobby argues that proportional representation allows people to vote honestly without fear of wasting their vote or letting in whichever party they like least.
But take the more than one-in-eight Liberal Democrat voters at the last election in Warwickshire. Under Jenkins' proposals, the county's existing five seats would become four single-member constituencies and one top- up seat. If the system had been in place in 1997, Labour would probably have won three of the single member seats; the Conservatives just one.
But with the Tories just five points ahead of Labour in votes, this means that the Tories would have been entitled to the top-up seat too.
In short, voting Liberal Democrat was a wasted vote - as it would be in 30 of the 78 mainland regions proposed by Jenkins. So also, of course, was voting Labour. Which leaves Labour voters with a conundrum, too. Might they be better off voting Liberal Democrat for the top-up seat to deny the Tories?
If one-in-eight Labour voters made that decision then the Liberal Democrats, not the Conservatives would win the Warwickshire top-up seat.
True, using the alternative vote for the single member seats will eliminate some of the need for tactical voting. Liberal Democrat voters will, for example, be able to put their local candidate first and then give their second preference to whichever of Conservative or Labour they dislike least.
But by recommending that the top-up seats be divided out in just ones and twos, the Jenkins system would create a whole new set of tactical dilemmas.
To make matters worse for reformers, some of the weaknesses of first- past-the-post would also still be present. For example, how many seats a party secures will still depend not just on how many votes it wins, but on also on where it wins them.
If the Tories' vote were to as evenly spread as it is now, then even if they managed to match Labour in votes, they could still be 60 behind in seats. And notice how Mrs. Thatcher's majorities would all have been a lot smaller than Tony Blair's.
The public is very uncertain about electoral reform. Now both pro- and anti-reformers have been given a tough task to win them over.
John Curtice is Deputy Director of the ESRC Centre for Research into Elections and Social Trends. He was a consultant to the Jenkins Commission, but is writing here in a personal capacity.Reuse content