Gym's in London

I'm moving to London in 4 days to work for at least a month (potentially two) at a bar or a hostel. In that time I would like to continue working out regularly as I have been at home. Obviously things like running and cardio can be taken care of outside but does anyone know any independent or chains that operate in the central London area (in particular near Victoria station) that offer either weekly memberships or no contract monthly memberships? Not looking for anything fancy, just a place with a decent weight room, benches and the lot. Pools would be nice but that generally ups the price on most gyms. Any info would be much appreciated.