He worked with people with learning difficulties and severe mental illness, and wrote on eating disorders in the elderly.

In 2006, the year before he co-authored his Cochrane review on screening for abdominal aortic aneurysms (AAA), he was appointed Regional Director of Public Health for the East of England, which he served until 2010.

[1][5] He completed his secondary education in 1981 and gained admission to study medicine at St Mary's Hospital Medical School,[a] London, where he also participated in rowing.

[4][7] Initially, Cosford had planned a career in general practice, but following the loss of a child to a genetic disorder, he moved to north west London to take up psychiatry and worked with people with learning difficulties and severe mental illness.

[3] In 1992, he co-authored a paper titled "Eating disorders in later life: A review", which was published in the International Journal of Geriatric Psychiatry.

[1][4] In 2006 Cosford was one of nine of the new Regional Directors of Public Health introduced by Chief Medical Officer Liam Donaldson, following the announcement of the reorganisation of the NHS.

[13][15] In 2007, Cosford coauthored a Cochrane review that established that men, particularly those over the age of 65 years, were more likely than women to develop an abdominal aortic aneurysm (AAA), and to prevent it rupturing and causing death, it was necessary to diagnose it early and arrange elective surgical repair of aneurysms larger than 5.5 cm.

[16] He reported that once ruptured, 80% died before reaching a hospital, and only half of those who received emergency surgery survived,[17] but by repairing them early deaths were reduced.

[18] The four trials in his review formed the basis of introducing one-time screening for AAA recommended by the U.S. Preventive Services Task Force.

[24] Subsequently, his career spanned the responses to ten new disease organisms, including Zika, Mers, monkeypox, and ebola.

[33] He discussed such screenings with the European Centre for Disease Prevention and Control in 2014, when representing the UK, he was appointed its new member.

[27] In 2014 Cosford contributed to the response to emergencies, including the contaminated intravenous baby feeds on maternity wards.

[27][50] Cosford was an active cyclist, having spent years cycling in London traffic on his Brompton folding bicycle.

[3] That year, he was lead author of an article in the Journal of the Royal Society of Medicine discussing lung cancer in people who have never smoked.

[55][56] The paper presented findings that lung cancer was associated with a stigma, and that the number of people with lung cancer who have never smoked was increasing, with outdoor pollution as a significant contributory factor, in addition to passive smoke and occupational carcinogen exposure.

"[3][4] In his emeritus role Cosford appeared frequently on national media to report regularly during the early days of the COVID-19 pandemic.

[4] Cosford was a fellow of the Faculty of Public Health,[4] and held an honorary senior fellowship at the University of Cambridge.