Audrey Hepburn was originally offered one of the major female roles in this film, but was committed to a stage play and had to turn it down. She ended up with a bit role playing a sexy cigarette girl instead.
The Swan & Edgar in Piccadilly, where Alastair Sim attempts to steal a pearl necklace, closed in 1982. Its subsequent owners were Tower Records, Virgin Megastore, Zavvi and since 2010 'The Sting' clothes store.
Audrey Hepburn receives an "introducing" credit, although she appeared in One Wild Oat (1951) that was released earlier in the year.
This film was the fourth-most popular film at the British box office in 1951 - according to the Wikipedia article on the film. However, Ben Mankiewicz, in his introduction to the film on TCM, stated this was the top box office draw of the year.