Hi, this is starting to give me some clarity. The information from the seller I was given when I bought this was that he was a relative of the original owner who had the bike refinished in original colour with some slight alterations, possibly the under BB cable guide, relocating the cable stop on the drive side chainstay and possibly the cable guides on the top tube. The work was supposedly carried out by an ex Holdsworth employee, the quality of the finish is excellent !. I would point out that the '531' decal is an 'up to' July '73 style, although frames used this after that date. The Shimano 600 groupset fitted is also supposedly original, as it is an early 3 bolt crank group from about 1975, when this groupset was introduced. It has all been well looked after, a credit to the original owner, who I cannot trace, at the moment.
On another note, reading back through this thread, I take it you are interested in other Holdsworth frame numbers. If so I have two more for you.
The first is the Mistral (#(0)60972, therefore 1984 build ?) I owned in the mid to late '80s. A sable brown frameset I bought from a shop in Enfield (sorry cannot remember the name) in about '86, along with a Chorus groupset, to built myself my dream bike ! Pics of frame label and me with bike. This frame was slightly unusual as it had a cage mount under the top tube. Unfortunately traded for a mtb in '92 as the craze picked up.
The second is one I am the current custodian of (#049831, therefore 1983 build ?). This has been refinished, and again is unusual with no lamp mount on the front fork.