Portobello Road came up trumps - a VERY clean 50mm f1.8 AF Nikkor for £40, which I haggled down to £34. It's the older type of AF with the motor in the camera body, like Pentax, which means that (a) it's full-frame not APS-C and will work on 35mm or full-frame digital and (b) the lens still has manually settable aperture, both fairly desirable features. The down side is that AF won't work on a few recent and lower-end Nikon bodies. I think it's in slightly better condition than the one I already have, except that it's missing the rubber grip ring for manual focusing for some reason. Whatever, I'll get some test shots and see which is best, and sell the other one. REALLY annoyed that I paid £60 for the one I've got less than a year ago...
And got a nice job lot of lenses and converters on eBay for £25.50, which also included a Weston Master II and a nice ex-WW2 navigational computer (a specialised slide rule) which is destined for my own collection of weird scientific stuff.
later - already found a ring of rubber grip material the right diameter for the Nikon lens on a lens in the "job lot of crap no offer refused" box (current contends fourteen or fifteen faulty SLR bodies, mostly Minolta Dynax, various non-working flashguns, four very faulty lenses, etc.) which I'll probably try to sell a little later this year. I'm on holiday for a few days at the end of the month, don't want to list them until I get back. I'll probably offer say six of the nearly working Minolta bodies as a job lot, the real garbage can be one big buyer-collect box - I think that if I start for a penny someone will be mug enough to buy them at some price, if only to salvage the motors, prisms, and other fun stuff. And if it's only a penny they're still out of my flat...
more later - and there's a thread on the navigational computer here if anyone is curious
https://forum.keypublishing.com/showthread.php?125826-Navigational-Computer-MKIII
The one I bought looks to be in much better condition, but I won't know for sure until I get it.