No MCB, what killed it was the never ending series of delays and requests for more money and more time coming up against a new government with no more money and no more patience.
The only delays after the flying trials were completed and issues addressed was the knee jerk safety review because the MRA4 shared the name Nimrod with the unfortunate & sad events that happened in Afghanistan to another frame called Nimrod.
Perhaps it should have been pointed out to the safety review board that the MRA4 is a completely different aircraft.
I'm pretty certain the MRA4 if it had dropped the name Nimrod would be entering service rather than getting killed off.
Funny how they bent the safety rules to get the VC10's flying pax again though.