We did a gig at One Poultry a few years ago. It's a rooftop restaurant overlooking Mansion house junction. Lovely place to eat and have a party, horrible for a band. As has been said already, parking in central london is a nightmare. The worst part was the get in and out. Very small lift shared by guests and staff, as the kitchen is on the floor below the restaurant so in use most of the time. Get in wasn't too bad as it was a private party so was closed to the public, and we were early. Get out was very stressful. Owning to letting the guests out first we had to wait until they had all left. Then we had to fight (almost literally) with the rude staff who insisted in piling all the tables and chairs in our way, and every time the lift did arrive would fill it with the chairs and tables. They seemed to have a system to keep the band from getting any of our gear in the lift until they were finished. We noticed they would move plies of chairs in to out path, after we had moved them out of the way.
Bunch of Richards working there, at least on the night we were there.