It turned up. It's a real one. Q2388 (the Q is made from a 0 and 1 as usual) on the (real track*) fork although the frame is slathered in thick powdercoat so I can't confirm the number is the same on the BB shell. EDIT: it is, I exposed ir with a wire brush.
Bare frame is 4lb 2oz. Has 90s 531 decals
but it's a 1963 frame based on known numbers either side.
Has the old style 10mm seat bolt. Looks straight and undinged although the seat tube could do with a clean out - the seller had a very short post in there and it's a bit cruddy below. Threads good, headset cups not the tightest I've known but they did need the rocket tool. Track ends mercifully chunky.
Will get Argos to give it the paint it deserves and maybe build a road fork. Although it's been drilled for a brake, received wisdom is that a real track fork isn't great on the road - it's not designed for rough surfaces or for braking forces, modest as they are with a caliper brake.
Had various hipster parts on it which I'll sell to fund the respray. Good crankset, Gran Compe track wheels (I'll true them as they're not up to my standards) and fancy flat pedals. There's also a reasonable front brake and lever, an interesting 3T stem, and a 1" threadless alloy fork (rare) with a steel steerer. The rest of it is worn-out shite ;-)
*put my front track wheel in there and the 23mm tyre has 3mm of daylight between the tread and the groove in the underside of the fork crown. I wouldn't like to see a 25mm tyre in there.