Could something mechanical have occurred that distracted him which wasn't picked up on the examination of the aircraft wreckage. After all it was very badly damaged in several areas and therefore could have masked a problem which the AAIB haven't noticed as they have presumed it was accident damage rather than pre-accident damage.
Could there have been an ASI or altimeter problem after all I didn't find any mention of them asking the other pilot, or AH if they had experienced any issues with the aircraft and if so, had they reported them verbally or in writing to the maintenance company.
I also note that the existing maintenance company queried with the CAA the maintenance of the aircraft from the previous company. Do they not get all the records(log books/maintenance records) when the aircraft is transferred from one company to another.