I got a tattoo at parting of the waves 7 years ago, and although lawrence (the guy who runs it) is proficient, he's not the best around.
I got a 9 1/2 hour piece done by Bancha (the thai artist) at Studio81 in afflecks, and he was brilliant, he designed it and people always say it's one of the most intricate tats they've ever seen. I've got friends who've had work done over the road from afflecks (cant remember the name) and that's all been really good as well. I've heard good stuff about sacred art, and seen some brilliant work that they've done too.
Whatever you do, DON'T go to the place in selfridges.