With regard to the Irish border issue, there is a protocol on Northern Ireland (the „backstop“) which is annexed to the agreement and sets out a fallback position that will only enter into force if no other effective arrangement is demonstrated before the end of the transition period. If this happens, the UK will eclipse the EU`s common external tariff and Northern Ireland will remain in some aspects of the single market until such a demonstration is achieved. None of the parties can unilaterally withdraw from this customs union. The aim of this backstop agreement is to avoid a „hard“ border in Ireland where customs controls are necessary.  The UK launched formal exit negotiations by formally informing the European Council of its intention to leave the EU.