Danny,
If I understand you correctly the stop-end barrier was down, and only raised when the Tower controller suspected an abort. My own recollection of Jet Provost operations at Linton and Manby (in the 1970s) was for the barrier to be up for both take-off and landing, and only lowered for aircraft unsuitable for barrier engagement. Perhaps there was a change in SOPs following this tragic accident?
When I read your figure of 4800ft for Runway 13/31 at Leeming, my initial reaction was that it compared favourably with 10/28 at Linton (4400ft), but an old copy of BINA actually gives 4200ft for the Leeming runway.