[nomadking]

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Northern Ireland/the backstop

If no long-term trade deal has been agreed by the end of 2020 that avoids a hard border between Northern Ireland and the Republic of Ireland, and if there is no extension to the transition period, then a backstop consisting of "a single customs territory between the (European) Union and the United Kingdom" will be triggered.

• Northern Ireland will be in a deeper customs relationship with the EU than the rest of the UK; it will also be more closely aligned with the rules and regulations of the EU single market.
• As long as the backstop is in operation, the UK will be subject to "level playing field conditions", to ensure it cannot gain a competitive advantage while remaining in the same customs territory.
• The UK cannot leave the backstop independently, it needs to be decided together with the EU.

...
The single customs territory is basically another name for a temporary customs union and, if it were needed, it would ensure that completely frictionless trade could continue across the Irish border. But it would also prevent the UK implementing any trade deals with other countries around the world that involve removing tariffs on goods. That upsets supporters of Brexit, especially as there is no guaranteed route out of this backstop unless the EU gives its consent.

Withdrawal Agreement.

to apply unless and until an alternative arrangement implementing another scenario is agreed,