It wasn't the aux pump but the bottom hose sounds plausible, too, esp since I had to dig about at it to renew the coolant recently.
I remember it was difficult to 'get at' and I wish I'd jacked up a little more. That'll need looking at again asap anyway...
Thanks for all the alternatives folks

Edit: Nope, not coolant hose clip, thanks for that, though taking off the undertray and poking around doing up clips and rag-wiping was certainly a worthwhile activity given that I've changed oil (dare you not to spill anything), p/steering fluid and coolant within the last few weeks. Perhaps it could still be 'residual' though; some of the coolant drips were very 'freshly pink'...