Major Colin Metcalfe Dallas Enriquez was born in Uttar Pradesh in India in 1884. He wrote many books about Burma, as well as Malaya and Sri Lanka (known as Ceylon at the time). His pony books are the Khyberie pair, which are set in Burma. Both books are beautifully illustrated by K F Barker.
Finding the books
Both titles are easy to find. They can be expensive because of their illustrator, but reasonably priced copies do turn up, particularly if you do not mind a copy without a dustjacket.