IIRC there were two JP accidents during low level aero display practices, both at Linton. One involved the barrel roll, shown at Post 27, where it was thought a poor horizon led to the pilot not raising the nose enough before he started rolling, with the result that the aircraft descended during the second half of the manoeuvre, leaving insufficient height to recover.
The other accident was again when an aerobatic display practice was flown with a poor horizon, this one involving a stall turn. The pilot pulled up with one wing low and attempted to stall turn towards the high wing. The stall turn was not completed with enough height for the pilot to pull out of the ensuing descent.
After the first accident barrel rolls were banned for a while. After the second stall turns were banned for a while. The real lesson is not to practise low level aeros unless the weather conditions are suitable, for authorising officers to take weather conditions into account and for nobody to put pressure on them to get the job done in marginal conditions.