Cold tap has started to drip. Taking the cover off, I can see the brass mechanism and that it can move a bit. That seems to be the issue.

Got in touch with Caple - they don't have any spare valves. It is, apparently, obsolete.

Searched around and see mention of 1212R-C as the thing I need - but with all sorts of descriptions. Franke Zurich being most common. Eventually find this:

Valve Cd 1/2 Cold SUPERSEDED BY 3683R - VLV 1212R C - DISCONTINUED

And then:

Bristan Beeline Valves 3683R

Never having replaced a valve, I am uncertain as to what will fit what.

Does all this mean that I can get any 1212R-C or 3683R valve and fit it? Or will something be horribly wrong like the splining?