David was born in Southport in 1932, the youngest child of Joan and Gerald Allen and a little brother for Elizabeth. He was 7 when war was declared and from Bilton Grange Prep School he spent his holidays in Scotland where his grandparents had been evacuated. David gained a scholarship to Rugby School and after specialising in Classics there, he went on to Clare College, Cambridge, initially to read Law, as both his father and grandfather were solicitors. Realising the law wasn't for him, he switched to Archaeology and Anthropology, but spent most of his time on his real passion, Plant Taxonomy. He didn't have a degree in botany and unfortunately he later discovered this would not have barred him from starting his career in the country's principal taxonomic institution at Kew. 

Consequently, on graduating David tried a variety of careers and ended up in Market Research for 8 years - one of his contributions was a report entitled 'The Future of the Wardrobe', an ironic subject for somebody who was uninterested in clothes or fashion! During this time, an idea for a book developed, so in 1965 he plucked up the courage to write full-time and in 1967 his book 'British Tastes' was published in an unexpected blaze of publicity; a full page in the Sunday Times, 7 television appearances and a huge amount of review coverage. 
This 'journalism' was all rather embarrassing for David as, by this time, he had changed careers again and had joined the Economic & Social Research Council, mingling with the top echelons of Academia. He worked for the ESRC for 19 years, during which time he founded the National Statistics Users Council and, most importantly, he helped to set up a national computerised Data Archive, which became a large and flourishing operation at the University of Essex. This resulted in his award of an Honorary Doctorate from that university in 1995.

In 1969 he published 'The Victorian Fern Craze' which acquired something of a cult following on both sides of the Atlantic! David had always been interested in Natural History and his passion for botany with his experience in social anthropology led to the publication in 1976 of 'The Naturalist in Britain' which was well received by historians of science. The book gained him election to the British Society for the History of Science, to the Presidency of the Society for the History of Natural History, who awarded him the Founder's Medal in 1998 and the John Thackray Medal in 2005, and to the editorial board of the journal 'History and Philosophy of the Life Sciences'. It also played a major part in David obtaining, in 1988, a PhD in the History and Philosophy of Science from Cambridge. 
In 1986 he took early retirement from the ESRC and approached the Wellcome Institute to teach on one of its Master's courses, which led to his appointment as Honorary Lecturer in the History of Biology. He also obtained a grant to pursue, what for him was a new field, the History of Medicine. By chance, the Wellcome Trust were looking for someone to run its History of Medicine Grants Programme and, due to his diverse career, he began 10 happy and fulfilling years as Co-ordinator of the grants programme. 
David had been involved with the Botanical Society of the British Isles in one capacity or another since he was a schoolboy and in 1985 he became President for 2 years, which coincided with the publication of his book entitled 'The Botanists', which was the official 150 year history of the Society. His years of extensive study contributed to the award of a medal by the Linnean Society in 1981 and he was made an honorary member of the Botanical Society in 1994. 

David was often asked to review new publications and he spoke at several conferences overseas. He published 9 books of his own, including the ones already mentioned, as well as 'Books and Naturalists' in 2010, which was number 112 of the world famous New Naturalists Series, now numbering 140 editions, which has been running since the early 1950s. His last project was published this year on his speciality in the genus Rubus, more commonly known as brambles. Apparently the study of brambles is called Batology!