I've recently seen footage of Churchill visiting troops in North Africa and it got me thinking about the logistics involved in ensuring someone as important as this was kept safe when visiting such places. Obviously I'm not an expert and so the first reaction I have to this is that's an unnecessary risk given that Europe was occupied by Axis forces at this time and the North African campaign was still ongoing, but maybe it wasn't as dangerous as I think it would have been?
Churchill's trip to North Africa in August 1942 was probably the most potentially hazardous. He certainly passed through airspace where Axis aircraft patrolled including the Bay of Biscay and the Mediterranean. He could have taken a safer (from Axis activity) route via West Africa but that would have taken longer.
Planners would have relied on secrecy and mathematics to keep Churchill safe. Luftwaffe and Reggia Aeronautica patrols were limited over these areas, and Beaufighters could have been used in the Mediterranean to provide some cover (I am not certain if they were). Churchill's Liberator would have been very unlucky to have been interfered with.
Allied air forces by this time were patrolling aggressively from Malta, which had been under acute bombardment just weeks before. This would have helped pin enemy aircraft on defensive duties.
Probably a greater hazard than interception was the capriciousness of aircraft in 1942: it is not often appreciated that in World War II aircraft were lost to accidents all the time. Navigational errors, mechanical problems, crew inexperience and just bad luck saw thousands of air crew killed or just disappeared. Churchill's US-made Liberator would have had a top pilot and meticulous servicing, but the possibility of disaster was there any time a plane took off.
The purpose of Churchill's visit was to change the leadership of the 8th Army, which had been a great source of consternation for him for 18 months. As if to illustrate the above point, his choice for a new 8th Army leader, 'Straffer' Gott, was killed in an air accident at this time. The 8th's defeat at Gazala in June 1942 had been a great embarrassment for Churchill, at the time visiting Roosevelt in Canada (a trip he took in a battleship- a very safe way to travel as U-boats would have had a minimal chance of torpedoing a fast, armoured ship). He was moved to visit Egypt in August to put right the command problems with the Army ahead of Operation Torch, scheduled for November.