Thanks for getting back.
So I've attached some pictures, and added text to them.
I reckon the spout will screw off, like yours, or it might just be a quarter-turn "bayonet" style attachment - like light bulbs. I may or may not have to take the taps off the base posts to do this. Depends on...
Aaaaaaargh!
But you didn't say HOW you did it!
I have a similar style bath/shower mixer tap, different manufacturer.
The diverter lever comes off, and you can see the plastic shuttle. It has an o-ring at the top which shuts off water to the shower when the shuttle is pushed up, and an o-ring...
OK, I had a new TRV-4 fitted this summer, and as the heating only came on recently, I now realise it is VERY stiff to turn.
I've taken the head off. The pin springs up and down without problem. The head by itself will turn freely from 6 to *. But replace the head and it will only turn freely...