I'm afraid my knowledge of De La Rue decks is a bit too thin to give you an accurate estimate. The only things I could offer would be these:
* The damaged cards will decrease the overall value of the deck.
* It's not entirely rare for a card to be glued to the back of a box as a means to show what card back was packaged inside. I don't think that the difference in the face of the card stuck to the box will affect the value much - after all, it's the side that's supposed to be glued down and hidden from view in the first place. There's a number of reasons why that might be the case, the most likely of which being that the cards used for the boxes had pre-printed faces. It's similar to what the US Playing Card Company started doing a few decades back with their Congress brand - because they were offered in a variety of backs which changed frequently, they would pre-print the faces of the cards and store them, so when the designs of the season were decided upon, they could complete printing them more quickly. In this case De La Rue may have pre-printed the faces of these Wills scheme decks (they were likely used for many different designs, not just the Wills decks, based on their rather generic-looking Ace of Spades), so when card backs were needed for the Disney boxes, they could be used for that purpose - the backs were blank and ready to be printed, while no one would ever see the faces as they'd be glued to the boxes.
* The fact that the box is intact is a good thing - boxes often tend to wear out before the decks do, and a good-condition box can enhance a deck's value.
* Another enhancement to the value is that it's a Disney collectible, meaning it's of interest to both playing card collectors and Disney collectors.
* As a British product, if you offered it to collectors outside of the UK, you might find more interest as it would be that much more scarce out of the country, though there's also the chance that nostalgia value might make it more popular to someone in-country who owned or coveted a deck of these as a child.
Again, any attempt to guess at the value by me would be useless because of my limited knowledge. But more importantly, what value are they to you, personally? It's possible that might outweigh any financial considerations...
As far as what other people think - there's a deck that appears to be identical to yours though in slightly better condition currently selling on eBay.co.uk for a "Buy It Now" price of £84.95.
http://www.ebay.co.uk/itm/VINTAGE-1940s-DE-LA-RUE-ENN-Named-MICKEY-MOUSE-PLAYING-CARDS-MI-3-1-A-/351865063091?hash=item51eccac6b3:g:WIEAAOSw-CpYBAaWI usually prefer checking completed sales/auctions to get a more accurate value, as not everyone gets the price they're asking, but this item is uncommon enough that I wasn't able to find any sales completed recently enough to still appear in an eBay search. The deck on eBay sounds a little expensive to me - but as I stated, my knowledge is too limited to be accurate and I could be completely off-base.
You might also consider selling the cards in the "single swap" market, in which case you might get a few pounds each for the cards that are still in good shape, but it's considerably more difficult to sell off an entire deck one card at a time.