Day motels are very common in the USA and are reasonably priced. It is a lifesaver when neither have a place to use. I have several friends that use them with me.

I've not booked a day hotel for use for myself but I have met a female escort who was working from one. They mostly know what's happening and as long as it's not something horrific i.e. underage, animals, their fine. If you feel uncomfortable going in together, maybe go in at 10 to 15 mins apart.

Sorry, London isn't my area, but I've used day-rooms in hotels before for meets - for more obvious(?) male-female meets.

Tend to meet in bar/coffee area, both carry laptops, and paper notes, working on when the other arrives. Chat as normal when meeting anyone, talk of travel, meetings, projects. Finish drinks and move upstairs to look at notes, etc. I guess the key word is discretion, you may know what you’re there for, everyone else may guess, but you don’t need to advertise it?

One friend I used to meet, preferred meeting in a club – less pretence, more open, more honest. However that was pre-covid, post covid finding a hotel with day rooms is difficult, finding a club open during daytimes is almost impossible (please, someone prove me wrong )