Reply To: Linking Business and First class tickets

[SJ]

The two bookings cannot be linked onto one PNR and BA will not check the luggage through. Neither airline will owe you any protection if you miss the LHR-HND flight.

This means that you will need to collect baggage at T5 and transfer over to T3 to check in for the JAL flight. How much time do you have between flights?

I would be inclined to head down to London the night before.