I have recently had to try to convert something I'd written into American English. I got most things right (although I hadn't realised that 'whilst' and 'amongst' do not exist in American English.) There is one thing however on which I failed dismally, on more occasions than I can count. I did not observe the mandatory distinction which Americans (now?) draw between 'which' and 'that' as relative pronouns. 'Which' can only be used at the beginning of a descriptive clause; 'that' is obligatory at the beginning of a defining clause.
Thus I happily wrote sentences like, 'I looked at the method which had been used', which sounds perfectly OK to me. But 'which' had to be corrected to 'that'. Another example: 'She was a wonderful “doula” during the prolonged labor pains which (no - THAT!) eventually brought forth the child.' (But 'which' would be required in 'I picked up Basil's cat, which seemed to be uninjured.')
Do these sentences, as originally drafted, sound wrong to you? Does this rule exist in British English? Have I been guilty of error for all these years? I checked with Fowler, who certainly recommends that 'that' should be used to introduce defining relative clauses referring to inanimate objects. But he admits that there is currently no rule to that effect, and that 'which' is used in this sort of clause by many writers, including some of the best ones. Have things changed since Fowler wrote in 1928?