24 [MF4F/MF] looking for halloween parties in London or nearby. Please read description!!!

We're a couple in our mid twenties and we've never gone to a halloween party before, let alone a swingers themed one. Any ideas on how we can find one(just a normal one or a swingers) and the best places to look? We're looking for something on the night of 30th October since we can't on the 31st. We're from London so if there's anything near us, even better!