In 1930 he was recruited by the Czech arms manufacturer František Janeček, founder of the JAWA motorcycle company, to work as an engineer and a racer.

[2] At the outbreak of World War II, Patchett returned to England and started work under the auto-engineer George Lanchester at the Sterling Armaments Company in Dagenham, Essex, helping to gear up manufacture of the Lanchester sub-machine gun.

On his way out of Prague he managed to throw prototype samples of Janeček's new anti-tank device over the wall of the British Embassy.

[3] In 1966, the High Court awarded Patchett £116,975 (£2.75 million as of 2025) for the British government's use of the machine gun he patented.

Mr. Justice Lloyd-Jacob referred to Patchett as "a distinguished inventor and valued designer" in making the award.