No customs at all !! I didn't order these items in bulk, but in separate orders; just to keep a single order cost below than 50 GBP.
However, one order 'Mad Men season 1-5' costed me around 62 GBP, that too came without any customs from Amazon UK.
Generally Amazon US calculates custom charges in the checkout itself, but Amazon UK doesn't...at least for more than 100 Bluray items I have ordered from Amazon UK, there was no custom charge mentioned in the final order amount.
As I mentioned, items from Amazon US were brought by my friend from US, so no extra shipping and custom charge.
If you wanna check more on individual cost of the items I purchased...just look at my signature - My BluRay Collection link. I have updated cost of each item including shipping and everything..just to keep a track on my expenditure on these Bluray discs.