Thank you for your reply.
When I saw this Constructor the front half wasn't too bad having been stored nose first in a shed but with the rear end still sticking out in the open and, consequently, very badly weathered. Although, the concrete block had gone there were very substantial steel plates that had supported it and they were still welded to the chassis and body.
It had been fitted with a diesel and the cab and body were painted with a camouflage, black and matt green, scheme. Parked next to this lorry, in very poor condition, was the correct type of low loader trailer that this ballast tractor would have towed in it's army days. I should say it was located in a yard, reached through a archway, behind a garage in the main street of a small country town close to Wrexham and not actually in Wrexham.
It's a pity I didn't take a camera but I've always thought, with some justification, that bringing out a camera makes you look like a "tyre kicker" in the eyes of the person trying to sell the lorry. As it was, I thought that this Scammell would be difficult to get back to original so I didn't buy it. I wonder if anyone did.