Hi,
Can't find 'Barfod Blue' but Belmont Blue is also known as Boughton Blue, perhaps it's picked up other names too? Pictures of many named varieties on the link below

Here is a link that might be useful: National Viola and Pansy Society UK

Thanks for looking. I've seen that site. The flower of 'Belmont Blue' shown there is exactly like those of the plants in question. I think the 'Barfod' name is an error originating at Heronswood. (Since posting I have corresponded with both nurseries.).