Yes. Most of them will only accept UK issued CC. I have always bought topups on ebay-UK(never boght anywhere else), usually for less than than the value of the topup. The seller will just mail you the #. Of course, topping up/balance check is free from here. The last three 20 pound topups I bought only cost me 14 pounds each. You can't beat that if you ask me.
Here are some topups: Actually the seller I bought mine from still as some for 14 pounds.
http://search.ebay.co.uk/search/search.dll...p-up&category0=
Phones: Xiaomi Mi Mix 2, Samsung Galaxy A50, ASUS zenfone 3,
Sim cards: AT&T (Contract), 3 UK, Piranha Mobile