On 5 January 1947, he was granted an emergency commission into the Royal Regiment of Artillery, British Army, as a second lieutenant.
The Home Secretary Merlyn Rees appointed him Director of Public Prosecutions on the retirement of Sir Norman Skelhorn in 1977, with a brief to reduce delays in the criminal legal system.
Soon after taking office, he took the decision to prosecute Jeremy Thorpe, who was acquitted of plotting the murder of his former homosexual lover.
A perceived miscarriage of justice after the murder of male prostitute Maxwell Confait, and a subsequent critical report by the retired High Court judge Sir Henry Fisher in 1977, led to a Royal Commission on Criminal Procedure chaired by Sir Cyril Philips, which reported in 1981.
In 1989, shortly after his retirement, he co-wrote the Hetherington-Chalmers Report with former Scottish Crown agent William Chalmers, which examined ways to prosecute suspected war criminals living in Britain for "crimes of murder, manslaughter or genocide committed in Germany and in territories occupied by German forces during the Second World War," over which British courts did not then have jurisdiction.