actually info on
Peziza is
not scant - here is a key to all the UK
Peziza species - free and available to all

:
British fungi - Keys
unfortunately you will notice that the first thing it asks you is whether the spores are smooth or ornamented . . . . even knowing that it was on burnt ground doesn't necessarily limit you to the traditional "burnt ground" species
I'm afraid that without a microscope, the genus
Peziza (like 90% of the British mycobiota- and that's being optimistic!) is something of a closed book
cheers
Chris
I am prepared to look at carefully dried (fully documented!)
Peziza specimens - I may be able to give you a confirmed ID - I do this because I have nothing else to do

PM me if you have material