What fun...Lego brick barbeque! Unfortunately, results were somewhat inconclusive, but I'll report back anyway:
Plain white ABS brick - lots of smoke and sooty floaters. Not unpleasant smell. I know that this is ABS - just needed to watch it burn :)
Colourless transparent (clear) brick - some black smoke but no sooty floaters, slightly unpleasant smell, some frothy foaming. I'm assuming that this may be PC so will try Billy Hiebert's recommendation (thanks Billy).
Transparent light blue windscreen element - difficult to light and seemed to be extinguishing my pilot flame. Didn't really burn, but quickly formed a charred surface. Indistinct smell.
I think that Lego must be using more than a few polymer types / mixes depending on type / colour of element as 4 burns have produce 4 different outcomes. Unfortunately, I just don't have the necessary experience to differentiate PS, MBS, PC etc by smell, so perhaps the best route is simply to try various solvents until one works. Given that dichloromethane is the solvent of choice for PC, what should I try in the event that I'm dealing with MBS or PS for that matter?