Going on what you were told by the original owner its a black Holdsworth, looking at the frame its seems to be 531C with pump peg and no mudguard lugs, it seems to have a number similar to frames of the period. Looking at the history site only one frame matches that, the 1990 Falcon Holdsworth Pro. The Marlborough bikes did not come in black, too plain, and had no pump peg. But there the similarities end.
Unless Falcon did these as hand built frames with some options like the cable routing its difficult to see how that feature got there. I am also not sure about the seat stay caps too, as I think someone else pointed out. The bike was fitted with Shimano 105 group set and Wolber rims which often get mentioned in the articles on line. Your chain rings look different to these, but things get changed over time.
There are several adds on line if you google 1990 Holdsworth Pro and we have 3 in the data base, but as said before the frame numbers are of a different style. Its going to be difficult to see the detail around the frame lugs to make reliable comparisons so you could start by goggling other firms using 531C tubing with the same features as yours to see if any came with the through frame cables.
If you draw a blank on other firms I think you will just have to settle for the brief details the owner gave you. Most of the frames we have in this group in the database are in a similar state as very little is clear around that time in terms of the frame numbers found.
