I can only tell you what the situation would be like in Belgium. Over here, you'd win, because the guy is making a manoever. Doesn't matter if you were overtaking or not. He had to check if it was safe for him to do the U-turn.

He'd have to have a very good lawyer to win this one. Also adding to the fact that you are a so-called "weak road-user" (that's the term we use here for pedestrians and bycycles) is a definite BIG plus for you.

Over here a so called weak road-user can cross a street with his eyes closed, and if he gets hit by a car it's still the car user who is at fault. (except when the behavior of the cyclist can be proven, but how do you do that ?)

I'd definitely claim this one, it's a sure win. Of course, I'm not up to date on UK law...