Changing jobs will not work as he needs to get manning clearance and they won't give it if he's getting made redundant. ...
Just to add for the sake of completeness:
This is MOST unlikely to be helpful in many cases, but personnel who have been selected for redundancy remain eligible to apply to transfer between Services or between branches and specialisations within the Naval Service:
"Transfers will only be considered into areas of shortage in the current or future force, such as Operational Pinch Points (OPPs) and Critical Manning Groups (CMGs).... Opportunities are expected to be very limited."
He should refer to relevant official documents and consult his DO if this is of interest.
Good luck to him.