Timelord, the answer as given by Brian Miller once of Martin Baker, can be found in Journal 37 of the RAF Historical Society. (Brian Miller was the man who persuaded Embraer to put bang seats in the Tucano)
The V-bomber Saga
Martin had long been concerned about the lack of ejection seats for the rearward-facing rear crew members in all three V bombers. He had developed a rearward-facing ejection seat for the Valiant, demonstrating its practicability when, in 1960, ex-RAF parachute instructor, W T ‘Doddy’ Hay, made a rearward facing ejection from the back of a Valiant over Chalgrove. In the other two V-bombers, ejection seats had been installed for the test pilots only because it was intended that production aircraft would have jettisonable crew cabins that would be recovered by parachute. When it became apparent that these crew capsules had been abandoned, Martin lobbied hard to have ejection seats installed for the entire crew. When a Vulcan crashed on approach to Heathrow on returning from a flight to Australia, and only the pilots survived, Martin became incandescent. The RAF was fully supportive of his efforts on their behalf and the nose section of a scrapped Vulcan was delivered to Denham for the development of rear seat ejection – as a private venture. The pressurised cabin structure precluded the provision of separate hatches for each seat, which would have been the ideal, and instead Martin had to devise a way to eject all three crew members through a single, central, hatch. In typical style, Martin turned the challenge into an advantage by incorporating a command ejection system that would automatically sequence the ejections so that the rear crew could be ejected in the shortest time without risk of collision.
A special rig was constructed to demonstrate the concept. When ejection was initiated, the rear seat shoulder harnesses were tightened automatically to position the rear crew members for ejection. As they were brought back in their seats the chart table, which extended across the width of the cabin, was folded upward by cartridge-powered pistons, to provide leg clearance, and the central hatch was blown. The centre seat and occupant then ejected, allowing, the other rear crew members to cant sideways and eject in turn through the same hatchway. Having proved the concept, the system was installed in the Vulcan crew compartment and was demonstrated very successfully to high level RAF and Ministry officials.
Incredibly the men from the Ministry decreed that ejection seats would not be provided for the rear crew of any of the V-bombers despite the availability of a very practical system. It is a matter of record how many rear crew members were condemned by this decision but what is not so clearly appreciated is the number of pilots who gave their lives by remaining too long with their aircraft while trying to give their crew a chance to live.