What is the title of a black white British film set in World War 2 with partisans trying to smuggle out a woman in a box or a coffin on a train?

What is the title of a black white British film set in World War 2 with partisans trying to smuggle out a woman in a box or a coffin on a train?
One believes there are several films and/or radio dramas on this angle. if this was a live woman, she would have to be on knockout drops ( Shakespeare rides again- Verona local??) I vaguely recall something like this- it would involve a baggage car where among other things, coffins rode ( Blind baggage) so-called as baggage cars normally have no windows but do have large side doors for bulky objects. I seem to recall a Prisoner of War or spy- almost an Amelia Earhart type character involved in this plot. There was such a movie.