The last time a British court convicted someone of treason the country had just survived the existential threat of Hitler’s Germany.

William Joyce, dubbed "Lord Haw-Haw" for the affected accent he adopted in his Nazi propaganda broadcasts, was hanged in 1946 for disloyalty against the country where he had spent most of his life.

Yet at the time, the conviction was not clear cut - partly because the UK’s treason laws are based on an arcane act from the 1300s, and partly because Joyce was in fact an American citizen found guilty on a technicality.

Joyce’s counsel also tried to argue the medieval law only covered crimes committed within the realm, whereas their client's treasonous actions had been committed in Germany. The arguments were not enough to sway the Old Bailey jury - nor spare Joyce the hangman's noose.

Seventy years later the debate over Britain’s treason laws has re-opened after a think tank report argued they should be revised to deal with the threat of jihadists returning from Syria and reflect the grievous nature of betraying one’s country.