50 Barcode Numbers
Bacodes beginning with 50 are the barcode numbers that come directly from GS1 UK. This is the only way to get these numbers legally, which means paying a joining fee and annual membership fees to GS1. Many people mistakenly believe that the country of origin of the barcode numbers corresponds with the country of origin of the product, whereas in reality products that come from the UK can have any type of barcode on them, and equally products manufactured overseas, or even made by overseas companies can obtain 50 barcodes through GS1 UK without issue.
This is a old myth that has been thoroughly debunked. Please see this Snopes article on the origins of this myth as well as a a debunking of it.
All barcodes and barcode systems are designed for international use, so there are virtually no restrictions based on the country of origin world wide. Any specific examples of stores placing any type of restrictions on barcodes can be seen here.