DerbyBorn wrote:

These sort of taps have a non-dismantleable cartridge that contains
the ceramic disks.
You need a new cartridge.

I suspected as much - though my dismantling could only get as far as
big lump of metal weighing about 700g, that I could see no way of
getting into!

http://www.shop.lunns.net/ceramic-disc-valves-42-c.asp

Thanks, but: if only...

Here's a picture of the tap:
http://galleryplus.ebayimg.com/ws/we.../1000x1000.jpg

The part I'm unable to dismantle is a great lump of metal nearly the
same diameter and length as the main body of the device shown in the
picture.

I'm not sure what's inside it, but it's a mixer tap controlled by a
single joystick that moves in two dimensions. Perhaps it's some weirdo
custom design that I won't find a spare part for, or perhaps inside
there's a standard part. But I can't get inside.

Daniele