I went to the Tank and Paddle for lunch yesterday, it's the old Agenda, underneath the London Underwriting Centre (Gotham City). Other than having a stupid name they also do pizzas that look pretty nice but the main benefit of going there is that they have this game.
You basically slide the weights on the wooden surface which has been salted to help the metal glide. You get points at the end of the game when your weights are still on the board which different scores depending on what zone they are left in. You play against another player so you can knock their weights off too.
Basically some sort of indoor bowls / curling on wood rather than grass or ice.
Also spotted these signs in the toilet, I don't think people are paying much attention to them