It's just too cold for a night out on acid in London. Ideally you'd postpone this for Summer and go to a park, or ideally, go to the country. You want seclusion, nature and quiet. Not fucking London...when it's freezing. Forgetting the temperature for a moment, London is a pretty intimidating and disturbing place on hallucinogens. It's bad enough when you're sober. Bad trip could easily rear it's ugly head. Happened to me on shrooms. I'd definitely reconsider.
Check out Corsica studios though, message me and I might be able to get you on the free list. It's got a relaxed vibe and if you're intending to smoke bud, It's totally cool to do it in their smoking area. Done it countless times with no hassle. A party would be ideal though, but there's no guarantee of that if you're not from around here. Best bet is to accept that you wanna be with nature and I'd recommend heading down to the New Forest in the summer. Ahhh...just thinking about it makes me wanna do it again.
Science Museum could be crazy though?