Yellow tiles? That's actually a bottle of washing up liquid. I'd no idea you were blind as well as frustrated comedians.
Anyway, I did, of course, lubricate the O-rings, I'm not a complete moron. The problem stems from the fact that they're the wrong size. Hence this post.
Also, I have tightened the nut under the sink as much as I dare. It's possible that that there is a rubber gasket missing between the tap and the sink, nothing would surprise me in a house where the mortise locks have been fixed in place with silicone caulking. I have bought a cheapo tap as a replacement, because, although I still reckon it's a nice looking tap, we're moving in three weeks. So if you want to come round and treat the fence, go ahead, I can't be ***********ed.
If I'd wanted plumbing advice I'd have asked for it. I was wiping lead joints before most of you were able to wipe your own noses. All I wanted was help in identifying a tap.