I am trying a different tack - I contacted my supplier, a local plumbers merchant, after finding the brand and model from my Invoice. The tap is guaranteed for 10 YEARS! So I'm not going to mess with it anymore in case I invalidate this.
I have isolated the supply and stripped the tap down to a blue plastic ratcheted thing from which the lever mechanism comes out. I cannot undo or pull this out (the retaining nut has been taken off, there is nothing visible I can remove or undo other than this). If I can get this out I can then...