What is the official reference document regarding VAT, taxes and customs?

Reference documents regarding VAT, taxes, and customs are specific to the governing local tax authorities.

A selection of links are provided below for your convenience.

Norway: https://www.skatteetaten.no/en/rates/value-added-tax/

UK:https://www.gov.uk/vat-rates

EU:https://europa.eu/youreurope/business/taxation/vat/vat-rules-rates/index_en.htm