So this weekend's news was welcome: Mr Blair now plans to stick to his predecessor's pledge and let voters decide whether they want to elect MPs by PR. Should we rejoice at the conversion of a leader whose party has traditionally preferred to slug it out one-to-one with the Tories? Is Mr Blair, like William Gladstone, one of those rare politicians who grows more radical with time?
Sadly, the truth is a little more complicated. First, of course, the Labour leader has offered only a plebiscite. He, apparently, remains opposed to PR. And his decision to back a referendum is certainly not born out of a love for multi-party democracy, nor indeed a wish to see the Liberal Democrats as a long-term force. It may suit Mr Blair's purposes to have the Lib Dems bag a good few (formerly Tory) seats. He might need Paddy Ashdown's support should Labour fail to win a large majority and he finds himself dealing with a small but truculent rump of left-wing rebels. But Mr Blair, in the long run, wants Labour to occupy Lib Dem territory as well as his own, and so he would prefer not to guarantee Mr Ashdown's party a long-term role by giving it the electoral reform it needs to have any prospect of wielding direct power.
So what is Mr Blair up to, so soon after Labour and the Lib Dems were lacerating each other's throats during last month's Littleborough and Saddleworth by-election? The logic goes like this: when the General Election finally comes, Labour's big lead in the polls could easily melt away. Mr Blair must, therefore, make sure that Labour remains seductive to Liberal Democrat voters. They must be persuaded to switch tactically to Labour in Tory marginals where the Lib Dems stand little chance. The bait is the promise of a referendum on PR.
In short, Mr Blair's agreement to support a referendum is a mark of Labour's continuing electoral weakness, not a sudden change in his beliefs. He may have counted the many ways in which such a referendum could eventually be sabotaged. We do not know what the question would be or who would frame it. If the Labour Party urged a "no" vote, the campaign for reform would probably be defeated, given Tory antipathy to PR.
So, like the relationship between Labour and the Lib Dems - which inevitably veers between intimacy and animosity in turns - expect positions on PR to shift constantly. In this area, we can be sure of just one thing: those voters who want a changed electoral system should not rely on Tony Blair to deliver it to them.