We need to be careful here with what was briefed and what was flown. I too have 2500hrs on the Buccaneer and am a QWI. Wainfleet Range, whether the target was 9nm ahead or 3nm ahead has no bearing on what height we should be at. The Buccaneer weapon system was analogue, which meant that there was a degree of lag in the system. The Control and Release Computer was driven by cogs, pulleys and string (believe me, I have seen inside one) - very accurate cogs, pulleys and string, but not as accurate as modern digital systems. As a result, on the Wainfleet Range Laydown pattern, which was flown downwind at 1500ft around Boston Stump, the crew would have been briefed to be at delivery height as soon as they levelled on the target run. The navigator would have been looking in at his radar screen trying to locate Target 3 (The Ship) at Wainfleet, which did not always stand out well on the Blue Parrot when the tide was out (which I think was the case on the day in question). Even in a visual laydown attack the navigator would be looking for the target on his radar to assist the pilot with sighting it. Also, as 45-25-25 states, the height check should have been undertaken at attack speed and height over the sea. The Buccaneer, at the time, had a strip altimeter in the back seat on the left hand side of the cockpit below the level of the navigator's thigh that was fixed to 1013Mb. To gain an accurate height check the navigator had to etch, with a thick chinagraph pencil, the height at which the height check was carried out. Most navigators are right handed, so this was also done below his thigh level with the 'wrong hand' - accuracy? Hmm! Try it. Sit in an armchair with a pencil in your right hand and try etching a line at 90 degrees to your left thigh on a piece of paper that is below your left hand side. Now imagine doing it whilst wearing an immersion suit, a skeletal harness and strapped into a bang seat!! So we used our left hands (easier but not as accurate as the right hand). What’s more, the etched mark was probably about 50ft thick.
Of course, pilots did wind the millibar sub-scale on their pressure altimeter to align it to the rad alt at the same time.
As a QWI, I never heard of anybody releasing practice bombs in Laydown below 200 feet, although I accept that that may have been practised for Strike options in Germany. The Navy were occasionally, however, a law unto themselves - I don't mean that as a criticism, but they were.
In my view, whether the Rad Alt had locked out below 100 feet, was temporarily unavailable because of the bank angle or had failed (or not), it was probably not the sole reason for the loss of the aircraft.