Why were Germans being interned, regardless of their political affiliation or opinions? In May 1940 Germany had opened up its western front, invading first the Benelux countries and then France, and this had put the British government on red alert. There was a fear that Nazi sympathizers might be lurking in Britain as a fifth column, waiting in anticipation of a German invasion and doing all they could in readiness for it. British intelligence was unprepared for the many tasks facing it at the outbreak of war. It had too few people in its ranks, and the reigning political uncertainty led to a rash turnover at the top. In May 1940 Winston Churchill fired the boss of MI5 and replaced him with Oswald Allen Harker, who was himself replaced by Sir David Petrie in April 1941. It was Petrie who reorganized the security services and was responsible for their many subsequent successes in the espionage war against the Nazis.

Great Britain had been accepting German refugees since 1933. There had been no doubt from the start that the Nazis wanted to erect a totalitarian, racist state, and by the end of 1933 already more than 37,000 people had left the country for reasons of politics or race. Some 2000 of these came to Great Britain. The situation worsened drastically in 1940 when Denmark, Norway, Holland, Belgium and France were overrun by the Germans and an invasion of Britain itself was feared by many.