Hey Grisgra,
I just got back from London and after doing the same research as you are, I wound up playing at the "Sportsman". Now, they had no poker there the night I played (neither did many other places as it was over X-Mas), but the place is professionaly run, clean and upscale.
http://www.thesportsmancasino.com/
GL - London is an awesome city!