Madnoel thanks for the suggestion, i looked at this, as you say it is an obvious place to start.
Had another look at this today, the pipe is joined at some point behind the dash, it changes to a clear slightly more rigid type tube wich runs all the way to the wiper mount on the tailgate. so don't spend 10 minutes looking for as black pipe
The pipe runs under the sill covers on the driver side inside the car, then over the rear arch and up to the roof, you can access the pipe above the rear arch through the jack storage hatch, it is just possible to feel the pressure in the tube when the pump is opperated although the tube is fairly rigid, it is easier to watch the air bubbles move slightly through the clear tube to indicate if it is blocked up to that point.
I traced the tube right to the wiper motor where it passes through to the outside of the tailgate. My plan was to remove the wiper motor to access the end of the pipe so could use a syringe to try clear any blockage (like a plunger). When i removed the wiper motor i found the pipe was kinked between the motor and the tailgate. I suspect the motor has been changed at some point and the pipe was trapped when the new one was fitted?
Anyway the bottom line is the rear washer is now working fine
, hope this information is useful to somebody else.