The wholesaler in question was Ron Kitching in Harrogate, their warehouse burnt down many years ago.
There are some significant manufacturing differences between these and the Tange made Kuwahara frames, most notably the quality of welding of the rear tiangle. Tange would pre-fab front and rear ends and supply "kits" to other companies to finish the process locally, back in the 80's it was a good way of avoiding high import duties on finished products. The lower quality rear end suggests that these have and the fact they have not been chromed or painted were probably the same build process, kits finished elsewhere and not in the Tange factory.