A very, very, minor point but one that may be of relevance to some.
If we leave the EU, then any goods ordered from Europe (not unknown to locate hard to find CD's or BluRays which don't get a UK release on Amazon.de) will no longer be exempt from import duty, due to VAT paid in Germany or wherever. These will be subject presumably to the £15 limit same as other "foreign" imports at which point UK VAT, import duty and the hated PO/courier handling fee will need to be paid.
That suddenly makes that €19.99 disc a much more expensive proposition.
Depends on the rate normally 20 euros would be under 15 quid.
But that assums that during the 2 year exit negoations neother europe or the uk thinks that preserving free or at least discounted trade is not something worth pursuing.
Which i think is extremely unlikley