Some of our websites are hosted in the USA. The bills in $USD for this are charged to my business Visa Card. The bank converts this USD amount to pounds GBP. For each transaction there's a foreign currency processing fee starting at 1 GBP and increasing with the value of the transaction. It is not listed as a separate bank fee in the bank statement so it is easy to overlook. This can represent up to 10% of some bills.
I've just been through our list of overseas suppliers and have changed the credit card on file to one of my Revolut Debit cards. There's no foreign currency transaction fee and it is at the Interbank Exchange rate. Less money to the greedy banks.