Leather did extensive research into integrated pest management of insect pests in agriculture, horticulture and forestry and he was a member of the UK government's Tree Health and Plant Biosecurity Taskforce. His work on aphids includes the discovery in pea aphids of cannibalistic behaviour. Leather has also carried out research in urban ecology, looking at the biodiversity value of roundabouts for over 10 years in Bracknell Forest. He was an advocate of the need for specialist training in entomology and taxonomy and before his move to Harper Adams University was concerned that his then unique (in the UK) Masters courses in Entomology, Integrated Pest Management and Plant Pathology would cease on his eventual retirement. In 2009 he coined the phrase 'institutional vertebratism' to describe the bias of scientific research funding to vertebrate animals, rather than the more numerous invertebrates.