This is the updated advice from HMRC on the movement of human remains or an empty hearse travelling.
Where a GMR is needed these should travel as freight. If a GMR is not needed these can travel as passenger.
For the moment, until customs controls are implemented, from NI to GB it is ok to travel as passenger whether the hearse contains human remains or not. All movements from GB to NI should be as freight.
For Republic of Ireland routes, a PBN is also required.