Could this be the Platonic film...?

"Trenchcoat" (1983)

Cast (in credits order), awaiting verification

David Suchet .... Inspector Stagnos Ronald Lacey .... Princess Aida Emanuel Abela .... Man at Museum Post Card Rack Margaret von Brockdorff .... Nun Ruth Borthwick .... Nun Freda Camilleri .... Nun Lilly Harding .... Nun Anthony Spiteri .... Bald Man Joe Quattromani .... Man in Fez Eddie Baldacchino .... Wheelman at Dragonara Casino Joe Coppini .... Fish Monger HARRY JONES .... Man with Duffle Bag

And to prove we're not lying... http://us.imdb.com/Credits?0086476