It's the retailer with whom the customer forms the contract under the Sale of Goods Act. This protects the consumer from having to jump through hoops and deal with uncaring big manufacturers like Nike, and enables them to raise a complaint quite quickly. Conversely, this protects factory outlets from dealing with your complaint, as you've discovered.
I don't think the new Inov-8 shop in Bakewell could be described as a factory outlet!