Bob Jackson Cycles responded to my email to say that s/n 10180 is one of theirs from the early '70s. I've done a bit more exploration to look for signs of transfers / decals with no luck so far.

[MENTION=57478]repechage[/MENTION] asked to see the frame with wheels so here it is. It is a 55cm ctc seat tube, 56cm ctc top tube and about a 100 cm wheel base. Centre of BB to ground is 27cm. (the measurements in inches are 21.5, 22, 39.5 and 10.5)

These measurements are very similar to the Le Croco I have although its wheel base is ~1.5 cm shorter than what may be the Bob Jackson. I think of the Le Croco as a crit bike, but I'm not sure if i'm right on that count. The wheelbase on the mystery frame is about 1.5" longer than [MENTION=61614]verktyg[/MENTION] 's Alpine so I don't know if that is sufficient to move the mystery frame into another category of frame.

Untitled by BJ Stevens, on Flickr

Le Croco - 1980's by BJ Stevens, on Flickr