Originally Posted by
CPH-Flyer
BA would very likely refuse to check you in with luggage, as you do not fulfill the criteria to enter Japan.
Your choices are, fly with carry on only, get the flights on a single PNR (BA and JL can be issued together) or switch the LHR to HND flight to a customer friendly airline....
or just fly JL or an airline that will interline on separate PNRs all the way