orbitmic

Could you tell us what you are trying to do? Interlining has multiple dimensions - ticketing, luggage, etc. BA interlines with the immense majority of legacy airlines luggage wise and probably nearly all of them ticketing wise, so in practice, you can get (very expensive) tickets combining end on end where no common fare exists. If you have such a multi-carrier tickets, your luggage can be through checked in the immense majority of cases.

Of course, as amply discussed elsewhere, if you are on separate tickets, BA's policy is no through checking, even where both itineraries are BA ticketed and operated.