The Warehousekeepers and Owners of Warehoused Goods Regulations (WOWGR) certificate is required for businesses to store duty-suspended alcohol. The importance of having a WOWGR license is that if a product is purchased via a WOWGR company, no duty will be paid until it is removed from their warehouse. They act as a custodian of your cask, while you would be responsible for any duty that is not paid.

You can find more information about taxes and duties here.