I'm coming late to this but I just wanted to add: there's a whole cruising 'language' in places like saunas that you have to learn so you can indicate interest or recognise someone is indicating it to you: people don't tend to walk up to each other and say "Hi, do you want to have sex?" (though that did happen to me a couple of times...)
If i wanted to find someone in a sauna I'd often find a free cubicle, leave the door open, maybe start stroking my cock and taking it out from under my towel, and trying to make prolonged eye contact with guys walking by that I liked (then a nod or smile to act as an invitation). Avoiding eye contact is a definite way of showing no interest. Touching your cock and balls lightly through your towel in the communal areas is also something that some guys do.
are you picky about who fucks you and whose load you take? If not, the darkroom is your friend.
Something I've also found here in Dublin, where there's also a pretty good sauna, is that some guys, for whatever reason (bi + repressed) can only let themselves have sex in the dimly lit areas like the steam room or dark room. I've had some super hot lads just by keeping my eyes open when in those areas.
Have fun! It's been a few years since I lived in London but Pleasuredrome was always a good bet and a good mix of different types of guys.