45 Cranley Drive, Ruislip which features as the Krogers' home, was their actual address in real life, from which they transmitted messages to Moscow. A second transmitter was found at the bottom of the garden in 1980.
Towards the end of the film, an MI6 intelligence officer called Blake is told that the Portland spies are due to be arrested. He goes to Lord's Cricket Ground in order to warn his Soviet Russian contact, but is recognised by other MI6 officers. The character is based on George Blake of MI6 who did betray secrets to Soviet Russia. He was arrested the same year as the Portland spies.
Houghton and Miss Gee were not filing clerks or even worked in the same office as portrayed in the film. She was a draftswoman , and he was appointed in 1953 as head of a clerical department in naval intelligence at the important naval research base at Portland after his supposed fall from grace at the British embassy in Warsaw. Moreover, as if to emphasize the fact that his career was not on the downward spiral after he left Warsaw (as the film seems to imply), he was even promoted in January 1957 to a better paid managerial post in the chief engineer's department. And at the time when he was in contact with the Russian agent Lonsdale (1959 onward) Houghton and Miss Gee would have been working in separate departments at Portland, and not in the same office as shown in the film. It was Miss Gee herself who was able to remove the required drafts from the office where she worked to pass them on to Houghton for photographing before they were destroyed as per departmental orders.
Made in 1963, but not released in the UK until May 1965.
Although it makes good cinema to portray Houghton as losing his position at the British embassy in Warsaw due to drunkenness, the real reason for his transfer back to England was more to do with bureaucratic reshuffles, in that the British government was economising on diplomatic service expenditure at the time. Houghton, as a married civil servant working in an overseas embassy, was entitled to a bonus of £1000 a year over and above what a bachelor in his position was earning, so it was decided by the Admiralty to replace him with someone unmarried.