I found this recipe on Jack Monroe's site so I'll post the link.
I wasn't totally sure about some of the measurements so I checked it against a BBC Good Food recipe (very similar but yes, Jack means tsp not tbsp) and ended up using that instead.
They stuck to the crumpet rings a bit so the edges look shaggy but, oh, they are scrummy. I think they will be featuring in breakfasts and lunches for the next few weeks.
They could be made thicker but this is the thickness I like.
Nearly forgot to say - very cheap too!