PS I'm getting a couple of bags of 'spent' mushroom compost cos I've heard people saying it can still produce mushrooms - any tips on what to do with it to encourage them?
The compost will of been used to grow agaricus bisporus better known as button, closed cup, open cup, or flat mushrooms according to what stage they are picked at. Usually you will get loads of mushrooms it just won't produce enough for it to be commercially viable anymore.
Place the compost in a container at least 4" deep with as much surface area as possible. Keep at 16-25°C water regularly to keep it moist but not wet & keep it covered with a sheet of cardboard suspended abobe the surface of the soil this variety of mushroom will not grow if exposed too light.
I would use a pump action mister bottle for watering rather than a watering can to avoid exposing or damaging any mycelium directly below the surface.