So I've got the spawn and looked up the really helpful growing guide on the Mushroom Box website. i finally understand what it's all about!!!
The spawn needs to inoculate the compost medium first and grow through it. Then, once the compost is full of mycelium (the little white fibre strands),
THEN that's when you put a load of damp "normal" compost on top to encourage it to fruit into mushrooms.
My compost bins weren't suitable as they are too big, airy and cool so I decanted some of the mostly rotted compost into some old plastic sheep lick containers and mixed in the spawn. Need to have a firm fitting lid and they now sit tight for a couple of weeks for the inoculation process to take place.
So - I am now at the stage that I have been before with kits....... the point at which previous attempts have always failed.........
I'll report back in two weeks