banned in sweden?

Can't give a definitive answer but the initial reception to this film was hostile, particularly from the media. They felt that John Mills should not have been cast as a villain, particularly a nasty German spy.

His traditional roles, even before the war were clean cut hero types.

Casting Mills as an evil spy and then making the spy a supposed Spitfire pilot just when the battle of britain and fear of invasion was at its height, must have touched some nerves.

It is possible that because Sweden was non-belligerent during the war and at the time of release being blockaded by the Germans, the government did not want such a blatantly propagandist film, depicting Nazis shooting civilians and hitting small children, to be seen. At that time German troops were free to travel through Sweden and Sweden was a major supplier of iron ore to Germany.

Additionally Allied forces had recently broken Norway's neutrality to try to limit Sweden's shipping of iron ore.

In summary, my guess is that Sweden was terrified of Germany invading them from either Finland or Norway and did not want Allied propaganda films to be shown.