It does make clunking noises going over bumps sometimes, which sound like the nuts holding the struts in aren't as tight as they could be and are moving up and down. I had the same noise on the Supra after getting new struts put in - so it could well be something like that (especially given the combined stimulus of a roundabout and a sweeping right hander, both taken at the limit of traction (nearly), and a bit of a bump).
OK, for now I'm going to pretend that that was it. Thanks!
[edit: it still seems to go. I'm pretty sure it was running when I heard the clung, in fact my first thought was that putting the handbrake on had somehow caused it and I always put the handbrake on before turning the car off. Dunno why. ]