Hey A great niche couple of london quality is Markos and Ms Artemis, have visited them twice and had a blast=) You can find the details on Ms Artemis page along with a link to the guys profile. Let me know if you find any other good couples:)
If you're prepared to travel a bit further, Kelly and Lerone near Leicester sound like a great couple, I've got a booking with them in July. Can't do the link on my tablet, but you'll find them on AW.