Well I took a look at it tonight. Sporterized. But it wasn't the typical No. 1 MkIII as I was expecting.
First of all, it only had 'sporterized' wood. Barrel appeared full length but he said the front sight was not original. Second, although there was part of the 'foot' style safety mechanism on the left side of the receiver, the real safety was on the tail end of the bolt, a lever on the right side of the striker piece. It had the sliding ramp sights, with the knurled knob on the right side. The receiver itself was very 'clean' without a bridge across the receiver (didn't appear to be milled away). The only marking on the metal band was B.S.A.Co, nothing else like No 1, Mk III, or any other cartouche, etc. The receiver was marked with one set of numbers; the barrel another. It said "For Cordite Only", but the barrel was also stamped Nitro Proofed. The front lower stock did have notches alongside the barrel channel where some sort of other hardward had protruded. It also had 3 unusual circular swivels(?) at the front, ahead of the magazine, and on the buttstock toe.
Bore looked fine, action itself appeared to be in good shape.
I don't know what the heck it is.
Grouse Man