OK, so I've tried it with the hooks..... massive crowbar on the end and a piece of wood as a fulcrum..... the keys have just started to pull through the metal...... that how much its stuck down. I can only conclude that its actually locked in place. Are there such things as locking manhole covers?
its not locked in place, its the weight of the concrete and the gods knows how many years its been since it was lifted.
you need to get a large hammer through flat screwdriver and chisel between the lid and frame. its time consuming but you will start making progress.
eventually you will be able to get the screw driver and start prising the manhole up, once at this point yo can use the keys to lift it