There are others more knowledgeable but I thought the Government had recently admitted the primary concern with MRA4 was airworthiness.
BINGO!
Heat, fuel and ignition source in the same zone without a fire detection system and means to put it out - that was a worry. Some idiot put a box critical to the flight controls at the back of the bomb bay - open the doors, one seagull and good afternoon. The fix for that was to limit the opening speed of the doors in flight! When the RAF engineers came up to do an audit of the work done so far they had to ask them to do it again due to discrepancies with the work, paperwork and oversignatures. We were asked to take delivery without a sonobuoy clearance - now wouldn't that be useful. Issues with controllability at certain weights, configurations and engine assymetry.
I used to watch the Requirements Manager, Capability Manager and 2 Group Desk Officers beat their heads against desks on an almost daily basis!
LJ