This thread may also be helpful. Ebay UK is probably the easiest. Don't think you can register a non-UK issued credit card.
http://www.prepaidgsm.net/forum/show...ight=virgin+uk
Phones: Xiaomi Mi Mix 2, Samsung Galaxy A50, ASUS zenfone 3,
Sim cards: AT&T (Contract), 3 UK, Piranha Mobile