Does anyone know if BA flights from HKG count towards the married sector requirement?

I can see seats from HKG-LHR on 5 April and 6 April on both of the BA flights on each day but I’m starting in Bangkok. Searching BKK-HKG reveals no CX flights on either day but if I call BA and ask for BKK-HKG-LHR using CX for the first leg and BA for the second would this work, assuming the reason is to do with the married segment issue, or does this only apply on CX/CX connections?

Can see RJ on the 6th BKK-HKG which would work fine but I wanted a “free” day in Hong Kong so was hoping for an earlier CX flight (there are several looking at paid availability).