Don't think it's a Holdsworth
I tend to agree with those that say it might not be a Holdworth, but then I also based that on thinking they didn't use nervex pro lugs, which has since been disproved. The angles look so shallow compared to modern racing irons.
On the lug front, a fiend of mine had a Mercian built, probably around 1975, and that was built with Nervex pros.
As an aside, my Mum and Dad both worked for Holdsworth, until approx 1955, when the married, left and headed out of London. My dream was always to own a Holdsworth. This I achieved eventually, owning 3... 2 of which I still have, albeit one is a Roy Thame, which as far as I'm concerned is a Holdsworth!