A mycologist with over 50 years experience in fungal classification and identification, which he now applies to criminal and civil forensic cases, mostly in collaboration with Professor Wiltshire. Fungal spores have proved to be a valuable extra source of palynological evidence, linking people and objects with places, and mould growths on human remains and other surfaces can provide intelligence as to the time of death or other events. Recognized as an expert adviser by the National Crime Agency (NCA), his skills have been used by 12 police forces, including 20 cases of murder, and he has appeared as an expert witness in five murder trials.
Director of the International Mycological Institute (Kew and Egham) from 1983–1997), he retired from a Research Professorship in the Universidad Complutense de Madrid in 2016. He is currently an Honorary Research Associate at the Royal Botanic Gardens Kew, a Scientific Associate at the Natural History Museum London, and a Visiting Professor at the University of Southampton, and the Jilin Agricultural University in China. He is Honorary President of the International Mycological Association, and has served as President of the International Union of Biological Sciences, British Mycological Society, and British Lichen Society.
Appointed Commander of the British Empire (CBE) for services to science in 1996, he has been honoured by various medals and other awards from learned societies. He is the author or editor of more than 50 books, on various aspects of the naming and classification of fungi and other organisms, evolution, environmental pollution, and ecology His research record includes descriptions of numerous fungi hitherto unknown to science.