Tuna is imported into the UK in plain unlabelled tins. The 'makers' just buy in bulk and put their own label on. So John West, Princes ,etc. and the own label brands are all from the same source.
Their are several different 'qualities' e.g. Flaked, steak, chunk, No drain , line caught but they all arrive in the country as plain tins and the brand labels are put on afterwards. Go with the cheapest one that is the quality you want.
Same thing applies to Corned Beef it is all imported in plain tins and the brand labels are put on here . It makes me laugh when I see people going for a ' Brand name' tin when the supermarket 'basic' one is from the same production plant bur half the price. The same labelling plant usually does the labels for several brands and just ships them out to each 'brand' to be sold on.