Good News - on rolling up my sleeves and investigating further, prior to my planned repair, it turns out that it was simply that the top of the final flexible hose had worked loose where it fitted onto the tap itself. The taps are a little loose on the basin and occasional re-positioning must have loosened things off.
A quick tighten with a spanner seems to have sorted things; I'll re-do the actual tap seating when I find my basin spanner...
In fairness to myself, I would have double-check the real (as opposed to 'apparent') source of the leak before I set to, but your reminder didn't do any harm ;-)
Right, what's next?...
Cheers Jon N