Never was the English Channel more important to this country than during the Second World War. More effective than any artificial barrier, it kept the British Isles safe from the humiliations and cruelties inflicted by the Germans throughout Europe and beyond. Safe, that is, for those fortunate enough to live in mainland Britain; nearer to France, some others were nowhere near as lucky.

Visitors to The Channel Islands: Occupation and Liberation 1940-1945 at the Imperial War Museum, London, can see for themselves what life was like for the few British subjects who fell under direct German rule during the war. Seekers after tales of repression and cruelty will not be disappointed; not, however, those looking to strengthen their belief in a population united in opposition.

The truth is that most ordinary people simply tried to make the best of it. This was seldom easy under an enemy administration as powerful as it was omnipresent. Against a background of German marching songs, well-captioned displays show how locals needed official consent for pursuits as basic as fishing or gathering seaweed.

Warning posters, such as that telling of a man shot for releasing a pigeon with a message for England, or of the execution of saboteurs, were everywhere. Stripped of men’s suits, the windows of the local Burtons the Tailor featured Hitler’s Mein Kampf and Twilight over England by William Joyce (“Lord Haw-Haw”), adorned with swastikas.

Some islanders, most obviously the Jews, were given a terrible time: the familiar yellow star and a notice stating Juedisches GeschAft (“Jewish business”) tell their own tragic tales. To help such victims of Nazi brutality was to risk everything. One particularly moving section recalls Louisa Gould, gassed in Ravensbrueck concentration camp for sheltering an escaped Russian slave labourer. A nearby steel whip, reportedly used on such prisoners, suggests her motives.

No wonder so many locals played it safe; better that by far than the sound of jackboots in the street and rifle butts on your front door. “They (the Gestapo) knock out of you all information with their third degree arrangements. You never know when it will be your turn next,” wrote one man in his journal. Polite but distant was the standard attitude towards the Germans.

Not for everyone, though: indeed, a few clearly got closer than was good for them. The illegitimacy rate soared during the occupation, despite threats of violent retribution for such “Jerrybags”. The exhibition makes it plain that informers were everywhere. Somewhat vaguely, a secret report tells of a woman having “her eyes (or her eyebrows) attacked with scissors”, possibly by a vigilante group styling itself the Guernsey Underground Barbers.

There was chumminess between the islands’ dignitaries, notably the Dame of Sark, and German officials (“With many thanks for a lovely afternoon,” wrote one in her visitors’ book). But nothing disturbs more than to learn of the list of names of suspected wireless owners an offence punishable by death that was sent anonymously to the Germans.

This atmospheric exhibition affords little comfort to those who imagine that, had the British been tested by occupation, they would have offered sterner opposition than, say, the citizens of wartime Paris.

“From the time the Germans landed we had to be very careful as to what we said or did, we were surrounded by spies and am very sorry to say many local persons in the pay of the famous (sic) German secret police,” wrote a resident later. One can only reflect on what might have happened had the Germans completed their Channel hop.