Further information: I have digital boarding passes for both the JER-LHR and LHR-OTP legs. I received them in the BA app after checking in and I also have them in pdf form as I am in the habit of getting boarding passes emailed to myself during online check-in too. I also have a physical copy of the LHR-OTP pass which was given to me at the gate upon my being reinstated on the flight. I used the boarding pass in my BA app to enter the gate at JER.