£65 a month with LA Fitness at their 'flagship' branch so you can use any of the others. It's a corporate rate. But it's a lovely gym. The classes are all included in the rate, they've got a pool that's big enough to do lengths in, a steamroom, sauna etc, nice locker-rooms and enough machines that I rarely have to hang around waiting for one to come free - 12 treadmills, 6 cardio waves, multiple bikes (upright and recumbent), cross trainers, power plates and lots of resistance machines and free weights. You get a free training one to one every 6 weeks or so to review your program too.
It's also got a spa attached which is sadly is v pricy but to be expected in the middle of Chelsea/Kensington.