No you can't, yes you can
MAN-LHR-LAX in F with overnight layover at T5 Sofitel. Not wanting the hassle of luggage in LHR I rang You First to make sure I could check our bags through from MAN to LAX. The answer, regretfully but firmly, was that we couldn’t. By way of elaboration, I was told it used to be possible but not any more. (Nice gambit there - the classic non-explanatory explanation).
So at MAN we were surprised when the agent offered to check us through to LAX. I was wary of accepting. (We have not forgotten, nor indeed forgiven - are you listening, LH? - the Christmas we spent in Goa with our possessions marooned in BOM, courtesy of a check-in agent who promised us she had checked them through to GOI). Somewhat apprehensively, we went with it.
Thank you, check-in lady. Nul points, You First. BA do indeed have a secure holding area in LHR and our bags duly turned up on the carousel in LAX. Which is handy to know… but even handier if you know before you pack.