With the bonnet fully open, the driver's side nozzles are reasonably handy to insert a trim removal tool ( or even an old credit card or flat screwdriver would do) and the whole item pops out. It can only come out about 4" (100mm) before the plastic water pipes and heater cable stop it. I didn't undo the cable or the water pipe to take it out completely but they look simple enough. Putting it back is simple, just a gentle push and it clips back in.
A replacement nozzle assembly of the 'curtain wash' design was quoted on a Utube clip as part no. 460955987A. That's as far as I got, except for a price off Ebay of around £18.00 for (I'm guessing) a non OEM part.
I'll look a bit further into it, I was thinking only doing the drivers side.