It's stated to be 1952 at the beginning of the show, but the letters retrieved by Tuppence from the kitchen waste bin are stamped with brown stamps bearing the portrait of Queen Elizabeth the Second.
Although the Queen's reign started in early 1952, stamps with Elizabeth II's portrait were only issued for the first time on 5 December 1952; up until that point, George VI s portrait was still on stamps.
Although the Queen's reign started in early 1952, stamps with Elizabeth II's portrait were only issued for the first time on 5 December 1952; up until that point, George VI s portrait was still on stamps.
A Morris Minor Estate Wagon ("Woody") is shown several times. This is supposed to be 1952, but these did not appear until October, 1953.
Near the start, the scene is a railway station in Paris. But the railway coach is very clearly a British one, belonging to the Great Western Railway. The fleet number 9112 can be seen - this is the Collett Super Saloon 'Queen Mary', at the Didcot Railway Centre, where the scene was filmed.