Still shouldn't have been £35 for me either though, I used the 15% off Screen Anime code.Just checked, and it was also declared as 39.99GBP for me for some reason. 34.99 would've made more sense. The value declared on the package that contained Birthday Wonderland did match the sale price of 19.99GBP. So perhaps it was just a typo in their system?
The declared value is supposed to be the purchased value.