I've also had the same suspect when I bought the penny in 9D, very very narrow to be UK E.Maybe they use modified last in width?Considering that in some markets, these shoes are available also in US E and EE width.
I think they are of same standard.Probably big stores with high volume could have better price from factories for their rebranded shoes.Fox example Shipton & Heneage is actually selling rebranded C&J shoes for 259 £
Grosvenor collection is made by Sanders, Bench-made collection is made by Tricker's
They are a pleasure to deal with, with quick customer service, and shipping is free within europe.
They also regularly send discount code via email.