As I was dismantling the inlet manifold for the cooling leak problem, I noticed that the throttle spring was missing (EAC8616). I don't know when it made its bid for freedom, could have been years ago for all I know. Everything works fine without it as there are other large springs on the butterfly spindle which make sure the butterfly closes.
Anyway, I have no doubt it is there for a purpose, so I thought I would order a new one. Its just a spring, nothing special, a large version of what you might find in a ball-point pen.
£40.90

Who makes up these prices? In fact, parts pricing in general is a complete gamble, some things being really cheap and others stupidly expensive.
I'm off to B&Q later, I'm sure I can find something that will do the job for a few pence.