What does that term "progressive" mean? It's a bit of a composite, one that strives to encompass social liberalism and economic leftism, environmentalism, multiculturalism, feminism and so on - an umbrella term, perhaps, for things that most conservatives dislike. It stands too for resistance to unaccountable and over-concentrated wealth and power, demanding that these things should be shared out and devolved for the benefit of the largest possible numbers of people.
If we accept that as a reasonable rough definition, who is the most progressive candidate for London mayor? The answer is not straightforward. Livingstone, of course, claims the progressive high ground and is calling for Green, Lib Dem and far Left sympathisers to join him there. He does so with some justice. In his GLC past he took the lead in campaigning against racism and for gay rights in the teeth of seething opposition. With public transport he championed and imposed cheap fares "on the rates", driving his enemies madder still by becoming popular for doing it. Today, the green lobby lauds him as a trail blazer in tackling climate change and seeking to restrain car use.
And yet, and yet...you know what's coming. Ken's been too business-friendly, too dictatorial, too centralising, too ready to accommodate Islamism and his environmentalism has been more about hype than achievement. I don't know about the last one, but all the others might be a bit worrying from a "progressive" point of view, even if you don't buy in to the Evening Standard, Nick Cohen or Martin Bright diagnosis of Livingstone.
Now we turn to the other candidates with progressive credentials of one kind or another. How do they compare? Well, Sian Berry is greener as you'd expect. She'd also like to see a 60 percent affordable housing policy brought in, which is more than Livingstone. In this, though, she too comes into conflict with progressives' desire for power to be devolved. Brian Paddick is much keener on this, in planning and policing just for starters. And then Boris Johnson comes into the picture. He says he's very keen to work co-operatively with the boroughs in just about everything instead of bossing them about like Labour's man. He also says he'd want his advisors to declare all their interest on the GLA website. It's not a huge step towards redressing the accountability deficit Livingstone's critics say he's run up - and we await with interest further announcements from The Blond on this - but it's something.
So what about social inequality - a key progressive concern? Which candidate seems most likely to correct it? This, perhaps, is the hardest question of all because there's a limit to what any mayor can do. For that matter can any mayor running a huge and growing urban hub of global capitalism be truly progressive at all? One final thought. I've now done the clever and helpful Vote Match test four times, each time answering certain questions differently. Each time I've been told that I'm a Livingstone voter. But each time I've found that I'm at odds with him or only just in accord with him on several questions. To win, he needs to prove his progressive credentials to a group group of voters in a variety of ways. Maybe he should have a go at VoteMatch too.