Allen earned the nickname "Bunny" from a Gypsy hunting companion in England for his proficiency in snaring rabbits in Windsor Forest. He was educated at Sir William Borlase's Grammar School, Marlow, Buckinghamshire.
He arrived in Kenya in 1927 to join his two brothers. He found work managing a farm for Mervyn Soames where he took guests out shooting. His bush expertise drew respect from the locals and he became a hunting partner of Denys Finch Hatton. He took part in three Royal Safaris including one where he captured cheetah by driving alongside them as they ran and jumping on their backs.
Allen returned to hunting in 1946 and through his famous clients on safaris was discovered by Hollywood where he acted as a technical adviser to MGM's King Solomon's Mines as well as The African Queen, Where No Vultures Fly and Nor the Moon by Night. He gained fame by working on John Ford's Mogambo and acted as Clark Gable's double during action scenes. See also White Hunter Black Heart.
- Allen, Bunny & Claassens, Harry The Wheel Of Life: A Life Of Safaris And Romance Safari Press, 2005
- Last of the Great White Hunters https://web.archive.org/web/20110629113345/http://www.salon.com/wlust/feature/1998/03/19feature.html