The hull of Sir Edmund was built by SeaSteel of Nassington, so it looks like the hulls were contract built and subsequently delivered to and fitted out at Norbury and/or Bunbury. I have, some time back, spoken to Jim Dyche and John Stothert? who were, I understand directors? of Shropshire Union Cruisers, later Dartline and worked out (from the hull number) that Sir Edmund was built early 1974. I have no meaningful history other than that and Dartline, in 1994 when I enquired, had kept no records of boats that had been sold out of the fleet.
This craft has the diesel tanks built into the swim (both sides, with a balance pipe) and was apparently their 'experimental' boat, whatever that means. All their boats had blue hulls completely down to the water line and were painted with 'epoxy' paint. The GRP tops were in white gelcoat. The 'parallelogram' windows were supplied by Severn Yacht (now defunct)
Do you have a hull number, scripted in weld, on the front of the weedhatch box?