In July 1940, Cooper was transferred to the 8th Company, 5th Totenkopf Infantry Regiment based at Oranienburg to the north of Berlin, tasked with training recruits in the use of machine guns.

Roy Futcher said Cooper claimed that "he had been in the parties that had rounded up Jews in Poland and thrown women out of top storey buildings."

On going inside the house he found in the top flat a bunch of these Ukrainians holding at bay with pistols some twenty Jews.

"[4]Thomas Freeman, a commando who had joined the BFC in order to disrupt it, said Cooper claimed that "He had himself shot over 200 Poles and 80 Jews in one day – by merely lining them up against a wall and shooting them down.

"[4] While Cooper was in the city of Dębica, one of duties of his unit was supervising Jewish and Polish slave laborers in SS-Truppenübungsplatz Heidelager, a concentration camp which was attached to an SS training area.

Cooper was awarded the Wound Badge in Silver, becoming the only Englishman to receive a German combat decoration during the Second World War.

He was transferred to the British Free Corps[5] and was soon promoted to Oberscharführer, assigned to a transit camp for new recruits at a villa in the Grunewald, Berlin.

[6] In November 1944 he was dismissed from the British Free Corps, arrested for "various heinous anti-Nazi crimes", and taken to the depot of the Panzergrenadier training battalion of the Leibstandarte Adolf Hitler, where he spent the next six months working for the Feldjägerkorps.

"[9] An appeal failed, but days before his scheduled execution, the sentence was commuted to life imprisonment "on the grounds that [he] had been [a follower] in treason rather than [a leader].

The Home Office and Security Service files on Cooper are held by the National Archives under references HO 45/25805 and KV 2/254 1939 Nov 01-1946 Jul 20 respectively.