Both prototypes subsequently crashed. The Victor at Cranfield when the tailplane came off while being tested for pressure correction at low level and the Vulcan at Syerston when it was oversped and broke up.
Dan Winterland, in Tony Blackman's book on testing the Vulcan, he casts doubt on this official report conclusion. He states that the crash Vulcan VX770 had been previously flown by Rolls Royce test pilots, who had carried out rolls, rolls off the top, and even a loop. After each aerobatic flight by Avro pilots, the insides of the wing leading edges were inspected for possible damage by a small-statured ground crew member, but Rolls Royce did not know of this, nor did Avro know of the R-R pilots' aerobatic activities at that time. Sometimes the nose ribs were found to be buckled and had to be repaired, but Rolls Royce were probably unaware of this and may not have been looking at the leading edges internally between flights.
He is of the opinion that the aircraft may have been severely damaged before take off for the Syerston display, and that that was probably the reason for the crash.