The US title of An English Murder is, The Christmas Murder (1951):
Synopsis from classiccrimefiction.com:
What would an English murder be? Why, it must be a murder of a kind entirely peculiar to England, such as are the murders related in this particularly ingenious novel. And, naturally, it takes a foreigner to savour the full Englishness of a specifically English crime. Such a foreigner is Dr. Bottwink who plays a very important part in the shocking events at Christmastide in Warbeck Hall. The setting seems, at first, to be more conventional than is usual in Mr. Hare's detective stories. The dying and impoverished peer, the family party, the snow-bound castle, the faithful butler and his ambitious daughter. But this is all part of Mr. Hare's ingenious plan, and there is nothing at all conventional about the murders themselves and the manner of their detection. In short, this is a peculiarly enjoyable dish of murder.
Read more about Cyril Hare and his crime novels, here.