Denmark's Oyster-ish system covers the whole country. Anonymous cards need a balance of at least 70kr to start a journey, and are limited to a region of the country — e.g. Zealand (Copenhagen's island) and nearby small islands. Adding the non-refundable cost of the card gives an amount larger than the longest journey within that area.

It's possible to set an anonymous card to a high advance payment (600kr = 80€), and then use it to travel across the country.

Great Britain is significantly larger, has much higher train fares, and isn't neatly divided into islands. They could limit it to contactless credit/debit cards, but I don't see a neat way to extend Oyster over the whole country.