Originally Posted by
Phoenixtinct
It is my understanding that as per OneWorld's policy if a connection is missed between OW carriers even if it involves separate tickets, the passenger is to be rebooked.
I’m afraid it is unfortunately a wrong understanding. AA have their own policy and AFAIK still do this, the rest explicitly do not.
If the op’s bkk-hkg is badly delayed and he misses the departure of his hkg-lhr the ticket will be lost bar (always possible) gesture of good will.