He was, unfortunately, wrong. Here's information about card restrictions:
What type of gift card do I have? - https://support.apple.com/HT204199
Redeem App Store & iTunes Gift Cards, Apple Music Gift Cards, and content codes - https://support.apple.com/HT201209
If you can't redeem your iTunes Gift Card or code - https://support.apple.com/HT201195
If you have a friend in the UK send it to them.