Gyzmo - I've had a breakthrough thanks to your advice.

I retrieved the shoes from the shop today and took them to a chiropodist/podiatrist (checked the spelling in the dictionary).
He thinks that the shoes aren't shoes at all but more like trainers (it's all to do with the shape and look of the soles apparently). He doesn't think they should ever have been sold as school shoes, on the surface they didn't look like trainers to me but I'm not an expert! Also you can see and feel where my sons toes have been inside the shoes so the quality of the inner isn't good either and even if the outer had been ok my son still shouldn't be wearing them apparently because they will damage his feet. Basically just wearing them for the time he has will already have harmed his feet. He had a full list of problems with the shoes/trainers particularly as I specified they were for school.
Another letter back to the shop then - he also advised to check their shoe fitting credentials and consider reporting them for the bad advice given.