The prop £1,000,000 note was larger in both size (about 7 x 9 inches) and value than any real note produced by the Bank of England up to that time, even notes for internal use. However, the bank still imposed strict regulations, which were violated when posters advertising the movie showed a reproduction of the note. This had to be covered over before the posters were allowed to be used.
Future film director Bryan Forbes can be seen as Todd, the tailor.
The £1,000,000 note at the time the film is set, 1903, would be worth approximately $100,000,000 ($100 millon) in 2002. Or £65,000,000 Sterling. In 2020, adjusted for inflation, the 1903 £1,000,000 would then be around £122,391,759.22. The film would still work remade in 2020 if the note was still an impressive £1,000,000. Although, after the similar "Brewster's Millions" & "Trading Places" story versions, the figure would probably be revised upwards to £1,000,000,000 (a UK Billion).
The plot for the 1983 Eddie Murphy /Dan Aykroyd comedy 'Trading Places' is loosely based on this film.
Although the film has Gregory Peck as the male lead, and its based on a Mark Twain story, the film wasn't made by one of the usual large major US Studios, as may be expected. It was produced by the J. Arthur Rank Organisation, at the time considered one of the UK's major film production companies. Although, obviously Gregory Peck's casting was likely with a view for the film to work well in the US market, as the source material was also American.