Originally Posted by
nth_utsera_sth_utsera
It's all at the check-in agent's discretion. I've often found agents at the F check in @ LHR T5 to be particularly poorly clued-up on this, so the default answer tends to be "No".
It's not that they are poorly clued up at all.
What you are seeing is the LHR staff correctly following policy, which is NOT to through-check bags to onward connections on non-OW operated flights, unless it is all on one ticket.
At the outstations, the check-in staff may (i) not know, (ii) not care (if they outsourced airport staff), (iii) be prepared to bend the rules, as the chances of getting caught/disciplined are minimal, compared with at LHR.