[Laurent Rizzotti]

At this time of the war, US heavy bombers flown to England will rather take the South Atlantic path (via Brazil - Africa - Morocco - England) rather than the North Atlantic path, from what I have read. So my first idea was that it could be such an aircraft, your man just being picked up as a passenger.

But it is unlikely that a crew on such a transfer flight went as far east as La Marsa, or even Algers-Maison Blanche.

If the 542 are the last digits of the US bomber, there are not so much possibilities:
B-17E 41-2542 (apparently never left the USA)
B-17F 41-24542 (survived the war)
B-17F 42-3542 (survived the war, was apparently in England at the time)
B-17F 42-29542 (apparently never left the USA)
B-17F 42-30542 (lost in August 1943)
B-17G 42-31542 (left the US on 25 November 1943 or later, arrived UK on 7 December 1943)
B-17G 42-97542 (delivered to USAAF in December 1943)
B-17G 42-102542 (delivered to USAAF in March 1944)
B-17G 43-37542 (delivered to USAAF in April 1944)
B-17G 43-38542 (delivered to USAAF in August 1944)

So three possibilities to search:
B-17F 41-24542
B-17F 42-3542
B-17G 42-31542: I will investigate this first, as it was in transit from US to UK roughly in the same time. But if you have confirmation that your man arrived in UK on 24 November, you can exclude it.