Under the “backstop” the whole of the UK would enter a “single customs territory” with the EU. There are many, but, for the most part, there would be no tariffs on trade in goods between the UK and the EU and some trade restrictions would be lifted (although not all of them). Paul Bew, a Crossbench peer, noted that the downward nature of the backstop reverses the ascendancy of the Good Friday Agreement, risking “the current deterioration of North-South relations increasing in unpredictable and dangerous ways.”  The Republic of Ireland is the second highest per capita domestic product in the EU after Luxembourg, thanks to a favourable corporate tax system and membership of the European single market.  About 85% of Ireland`s freight exports worldwide are from ports in the UK, about half of which are destined for the UK, while half continue to the EU via Dover and Calais.  The UK`s use as a “land bridge” is rapid (it takes 10.5 hours for the Dublin-Holyhead-Dover-Calais route), but could be compromised by customs checks in Wales and Calais in a Brexit without agreement. Indeed, in the absence of trade agreements, the trade relationship between the United Kingdom and the EU (including the Republic) would amount to membership of the World Trade Organization (WTO). They stipulate that the same tariffs and tariffs must be applied indiscriminately among all WTO members (the most favoured nation`s criterion), unless some members have a trade agreement.  This principle would also apply to trade across land borders in Ireland in the absence of a trade agreement. This is where the controversial backstop comes in.
Many MPs have criticised the backstop for two main reasons. That this would lead to other rules for Northern Ireland compared to the rest of the UK (which some considered the integrity of the UK) and that the UK would not be able to leave the backstop without EU authorisation. The Irish backstop (formally the Northern Ireland Protocol) is an annex to a draft Brexit withdrawal agreement drawn up by the May Government and the European Commission in December 2017 and completed in November 2018, which aimed to avoid an apparent border (with customs controls) between the Republic of Ireland and Northern Ireland after Brexit. The Irish government, in particular, insisted on this “backstop”.   Boris Johnson spoke out against the backstop and declared that it was undemocratic and that it could trap the UK on EU customs territory. In an earlier version of the piece, which was incorrectly stated, critics of the Irish backstop are concerned that “this will lead to other rules for Northern Ireland compared to the rest of the EU”, which should have been “the rest of the UK”. The DUP, a Northern Ireland Unionist party that currently has 10 MPs in the House of Commons, refused to accept the backstop because it could keep Northern Ireland in a different customs regime than the rest of the UK. The “Irish backstop” would come at the end of the transition period if the UK and the EU had not negotiated a future trade agreement that would have kept the Irish border as open as it is today. The Irish border has been described as a “backstop” by both the UK and the EU because of its importance to the peace process in Northern Ireland.
The Good Friday Agreement of 1998 was a key element of this peace process.