In the bar scene in Alexandria, John Mills was drinking real beer because ginger ale and other substitutes didn't look real enough on film. In the final cut (the 14th take) he actually was quite drunk.
When the ambulance crosses the minefield was just a few notes in the screenplay. It was improvised by director J. Lee Thompson into the tense sequence we see in the film today.
When Captain Anson tries to stop the runaway ambulance going down the hill - from the running board - there is clearly someone in the driver's seat in two shots.
Although Basil Hoskins's character is described as Corps of Military Police lieutenant, his cap badge is that of the Middlesex Regt. The NCOs are wearing the correct MP cap badges.
At the checkpoint when entering Alexandria, the MP Captain hands over a shirt saying "This is for your South African friend". Later Captain Anson states that he has told security that he has a German Officer with them. Anson is trying to conceal Lutz's assumed identity and would not have told the checkpoint captain that Lutz was South African.