What is the Northern Ireland protocol?

The Northern Ireland protocol, formally called the Protocol on Ireland/Northern Ireland, is the part of the Withdrawal Agreement with the EU that ensures there is no hard border between Ireland and Northern Ireland as a result of the UK leaving the EU. The protocol sets out the rules governing GB-NI trade from the end of the transition period, effectively moving the border into the Irish Sea rather than being on the island itself. It also contains a so-called ‘consent mechanism’ by which the Northern Ireland Assembly will vote every four years from the end of transition on whether it wishes to continue with the arrangements in the protocol.