Thank you for your responses.
I had tried Gumtree to no avail. There were one or two that took my interest, but replies from the owners seemed sketchy and the ads have since been removed. One never can be too careful.
Interestingly enough, upon learning of the new MIM prices I considered a Marcus Miller V3 or V7, then promptly demurred over the active electronics and flatter fingerboard radius. In different circumstances I would have bought one immediately, but at the moment, its electronics might cause more headaches than they'll remedy. Definitely a future prospect, though.
It does have to be a Jazz or something very similar, I need the honky back-pickup sound; also, I know them well and familiarity is crucial at the moment. I wish I''d been looking at the classifieds section much earlier today, this would have been just the ticket.
Good to know. The Bass Centre was the placed I looked to first, though as it's closed to normal trade, far from ideal. Although incidental to anything really, I am quite taken by Windermere Blue — always wanted something in a Lake Placid Blue-like finish, with matching headstock.
I didn't want to delay any further and managed to find a Squier VM Jazz (searches seem to suggest Squier has a fairly decent reputation on here), advertised with a rosewood board for £250 new from a reputable shop. Pending any hiccoughs, it should be here in the morning — I'll let you know how it is.