Where do London's singles meet?

My cousin is in London for a month and would like to meet new girls (early 20s).

I personally don't really enjoy nightclubs, so I have zero knowledge about London's club scene, but he is enthusiastic about starting his adventure there.

What would you recommend to this young man who is exploring the world? Any specific nightclubs?

Would especially appreciate advice from women and/or people without commercial interests in their answer.

Thank you