There are Disney Outlets. I'm from PA and we have a Disney Outlet in one our Outlet centers. They have Disney items, and there's even a section that has clearance stuff from Disneyland in CA, not Disney World in Fl.
That being said, if you want the authentic park stuff, you'll have to almost bite the bullet and pay what they ask for it.
The only thing that's close to offsite is the World of Disney store in Downtown Disney, but you're going to pay full price for things there.
Did you try the disneystore.co.uk website? Sign up for a newsletter and theres a few offers on right now.
In Ireland we have disney clothing in Penneys (Primark) and Tesco and New Look. The last two you can buy online from but they aren't quite as cheap. sportsdirect.com do very cheap disney clothing (type disney into search bar).
Your other option on clothing is to post on the creative board as some very talented DISers make personalised tshirt transfers. You just print them onto iron on transfer paper and iron them onto your tshirts, bags etc.
Hope this help.