Originally Posted by
CKBA
Maybe it was under the 'old' system - whenever that was, but I did a CHC-SYD (cash QF ticket) SYD-SIN-LHR (cash BA ticket) and LHR-IAD (BA avios) - three PNRs and had the bags checked all the way through (took them a while, but it worked!).
But, unless I am reading your itinerary backwards, that was QF who arranged the through-checking, when you started your journey at CHC.
QF agents follow QF rules, not BA rules.