The AAIB June bulletin includes a report on the accident to G-ATRR at Caernafon:
Air Accidents Investigation: Piper PA-28-140 Cherokee, G-ATRR
Amongst other things, the investigators found the rear wing spar attachment bolt ( or rather they didn't find it ) and some other interesting remarks include:
"A review of the aircraft’s maintenance revealed that the engine had exceeded its overhaul period by 1.7 years and there was no evidence to indicate that the actions required to extend this period by 20% had been carried out. There was also no evidence that a cylinder compression check had been carried out in the 229 hours since the last annual. The worksheets indicated that only a 50-hour check had been carried out when a 150-hour check was due, and investigations by the CAA revealed that this had occurred on two other aircraft owned by the operator. Further concerns about the maintenance of the operator’s aircraft resulted in the CAA suspending the Certificates of Airworthiness of eight of the operator’s aircraft."