They had four children and his elder brother, Meredith, was a professor at Leeds and Manchester Universities and also a Fellow of the Royal Society.
In 1971–72, Evans was director of the Lister Institute of Preventive Medicine and struggled in vain to save its Chelsea laboratory from financial failure.
He left in 1972 to become director of the National Institute for Biological Standards and Control to prepare for its 1976 move to South Mimms.
In 1976 he taught medical students at Oxford University in the Sir William Dunn School of Pathology until retirement to North Wales in 1979.
He was elected a Fellow of the Royal Society in 1960 and awarded their Buchanan Medal in 1977 for his leading role in the standardization and safety control of vaccines.