Well… ballot papers have arrived! Anyone know of a good tactical voting site for the London Mayor and Assembly elections?

It seems our previous SV (Supplementary Vote) has been taken away and replaced with FPTFP (First Past The F*in' Post) just to make things difficult and stupid, so now I need to see about voting tactically.

I would have put Green as my first pref (because the environment, particularly the climate, is the single biggest and most overwhelmingly important issue on Earth right now) and Labour as second (because they aren't the Tories), but I don't know if voting Green now might let the Tory in, so I need to find advice.