If you are in the UK and would like to trade on Amazon, you can get a UPC by registering with GS1 UK.
GS1 UK will generate a number of unique product codes for you, which are then accessible by other entities, machines and devices using the GS1 database.
GS1 UK will provide you with regular updates on ways to ensure your products and their barcodes remain standards compliant.
GS1 UK numbering and barcodes also operate as GTINs and EANs.
Silicon Dales recommends that UK-based merchants selling on Amazon use GS1 UK to generate barcodes and unique product codes.
If you are publishing a book, you will need an ISBN. You can order ISBNs from regional services.