Harry Houghton is shown signing the Official Secrets Act by the date "September 1950", establishing the time when he joined the Portland Underwater Weapons Establishment. But before that, while he is being driven to Portland, the cars in the background are contemporary to the film's 1963 production, specifically two early 1960s Ford Anglias and a Morris Minor with post-1956 styling.
If Houghton is signing the Official Secrets Act in September 1950 in order to join the Portland Underwater Weapons Establishment this cannot be correct because he did not finally leave the British embassy in Warsaw until October 1952.
The scene at Lords cricket ground uses a shot of stock footage of a match there. We then see a close-up of the pavilion, but it is clearly not the one at Lords. It was probably filmed at another, smaller, cricket ground in the south-east.