Does anyone have experience playing London MTTs?

What kind of level is the play or is it massively varied?

I'd assume that, aside from the accents, they aren't much different than those here in the US. There will be various skill levels and betting styles, and they will be nice people to spend time with.

Yes, and it is no different from any MTT elsewhere, you will get good & bad standards. But everybody pays their money and has their own way of playing. You cannot control how others come to their decisions, you can only control you, and as long as you minimize your mistakes you should do well, no matter what city or room you play in.