C. E. Heanley

British author. Full name Charlotte Elizabeth Heanley. She wrote a handful of adult novels (I think all historical) and one children's novel, which is perhaps more of a general animal story than a pony one, although I have included it as it does feature a horse.

Pony Books:

PETER AND CO
(COUNTRY LIFE 1937)
ILLUSTRATED BY FRANK HART
SUMMARY: Animal and pony story set in Suffolk.

Collectors info:
Peter and Co was not reprinted at all as far as I know. It  is reasonably easy to find in the UK and not usually very expensive to buy. Can be much harder to find elsewhere and a lot more pricey.