Sara Allgood
I was surprised to learn from the DVD audio commentary that the only member of the cast Ford didn't like or get along with was Sara Allgood, nor did Ford like her performance as Beth Morgan - supposedly he even criticized the very Irish Miss Allgood for not cutting bread like a real Irishwoman! (It's also mentioned on the commentary that Ford didn't seem to care too much that VALLEY was set in Wales and that its characters were Welsh, and definitely gave it an "Irish" slant - little wonder that many a Welshman has been offended by this film through the years.)
Personally, I disagree strongly with Ford - Allgood's performance is one of the finest in the film, and moved me to tears more than once, often without her saying a word - she had an extremely expressive face and body language. She and Donald Crisp were perfectly matched as a couple who had been together for many, many years (it's also made clear in the novel that the Morgans still have an active "romantic" life) - their affectionate bickering (such as "Ah, go and scratch...") comes across as completely natural. It's a shame that Allgood didn't win the Best Supporting Actress Oscar for which she was deservedly nominated.
"I don't use a pen: I write with a goose quill dipped in venom!"---W. Lydecker