Ok, The Apple Store genuine adaptor charges correctly (as you would expect) and on the iPad is the battery Image and percentage charge showing as you would also expect.
The adaptor I was using was a non-apple UK supplier wall socket mains adaptor. That is now in the bin.
Out of interest I also used the supplied US 110v adaptor in our UK shaving socket set at 110v and that also showed the battery image and percentage charge.
Morale of the investigation- only expect perfection when you buy only Apple products, through and through.
PS I did read you links ahead of commenting. What was confusing was the power going via the non-apple wall socket mains adaptor was not correct but one would assume they would be identical , but they are obviously not the same wattage power.