The film was made at Elstree but a unit went out to Belgium to film various outdoor scenes. The film unit based themselves in Leau, a small town with a population of 2,000 about 45 miles east of Brussels. Some of the scenes were at the Château de Sterrebeek, just outside Brussels, which stood in for the Château de Malvines in the film.
Nicole's piano is an Érard. Franz Liszt is said to have played a six-octave Érard piano in Paris in 1824. Érard put him under contract from about this time until 1825, so when he toured England they sponsored him and he played their pianos.
Von Hohensee's piano is a Bechstein. Carl Bechstein made pianos able to withstand the great demands imposed on the instrument by the virtuosi of the time, such as Franz Liszt.
Marius Goring could speak fluent German, particularly 'high German' and French.
The Liszt that Nicole is practising when the commandant comes into her sitting room is his Piano Sonata in B Minor. S.178 Cantando espressivo senza slentare.