Hi Nicolev
It depends on what you are looking for, what night of the week and where in London you want to be.
Assuming we are talking the centre of London you could go for a guest list at a club like China White or a bit more low key like drinks at Floridita on Wardour Street.
Hakkasan is one of my favourites - great atmosphere and good food and i have been to a few parties there and they were really good - amazing cocktails.
If you want more ideas let me know
Happy birithday