Are Wheelchair Accessible vehicles normally fitted with a manual interior (emergency) door release on the inside of the tailgate (On my 2008 Doblo)
If you have any expeience of dealing with these please see my Technical Query
This problem now fixed!
I managed to release the (seized) Bowden cable attached to the inside of the tailgate lock - this has now allowed the tailgate lock to work normally - like it has done for over twelve years
I was very lucky that I had already removed the inside plastic cover for replacing the wiper motor recently as the position of the interrnal folding wheelchair ramp would have made this quick fix almost impossible to access.
Looking at the other posts, Youtube videos (none) helped me evolve a solution
thank you for looking!