At 46 Terry-Thomas was a year older than Hugh Griffith, who played his father. Jean Anderson, playing his mother, was only 4 years older than Thomas.
Kingsley Amis felt that Terry-Thomas was miscast as Bertrand Welch, but decided he was so amusing in the part that it didn't matter.
The road outside the hotel (in the scene after taking coffee) shows lines of trolley buses on both sides of Broad Street in Reading: in 1957 they were the backbone of public transport in the town. The Boulting brothers attended Reading School, which was then and still is a grammar school originally founded by Reading Abbey in about 1125.