John was born in Portsmouth, the younger son of Vice-Admiral John Derwent Allen, C.B., and his wife Ruth Allen Atkinson Willes.

He was educated at Lancing College where he won an Exhibition and was in Seconds House from September 1931 to July 1936. He was a member of the Running Team from 1934 to 1936 and a member of the athletics Team in 1936. He edited Lancing College Magazine from 1934 to 1936. He was a member of the Officer Training Corps achieving Certificate A in 1936. He was appointed as a House Captain in 1935 and as a Prefect in 1936. 

He Matriculated in 1936 and read classics. He graduated with a 2nd in Classical Mods.

He was gazetted on 5 July 1940 and posted to the Duke of Cornwall’s Light Infantry. He was seconded to the Nigeria Regiment Royal West Africa Frontier Force which went to Burma in 1943.

John was killed in action on 25 January 1944 and was buried in the Taukkyan War Cemetery Plot 10 K 9.

His address was Red Cottage, Townsend Avenue, St. Albans. Hertfordshire.