Well, I went into the workshop this morning and watched the engine come out and the cam belt covers come off. The engine never left my sight.
A few interesting observations:
Firstly, when the pistons were aligned to TDC it was actually the right bank, not the left that had jumped a tooth on the inlet cam.
Secondly, there was a very obvious nick in the belt, suggesting that the damage had been done by a stone.
Thirdly, the belt tension on this bank was within spec (202 Hz). Ironically, the belt on the other bank was out of spec (150 Hz), although it had not jumped a tooth.
So I have to recognise that there was no faulty workmanship 10 months ago. We have decided to obviously replace both belts and to replace both tensioners and bearing assemblies. We're also replacing the alternator belt whilst the engine's out.
I should have the car back on Thursday afternoon, albeit some $4,000 poorer......