Been a few times... TBH it's as 'scary' as you want to make it; mostly it's fancy dress for grown-ups.
Some of the stage shows are quite intense, and there's often some action in the 'dungeon'. But if you want you can just dress up like a tart and dance to hard trance and breaks all night.
No one will molest you (not without asking your permission first anyway

, and if they don't, they will be thrown out with all haste if you complain - the number one rule is CONSENT!).
If you want to meet some people first, go to a fetish 'munch', a non-dress-up drinkies/meet with people somewhere chilled -
www.londonfetishscene.com will direct you to one near you.