Boris Johnson accidentally made an incredibly compelling argument against his own Brexit deal

Daniel Leal-Olivas/Pool via REUTERS

Britain's Prime Minister Boris Johnson helps quality control staff during a general election campaign visit to the Tayto Castle crisp factory in County Armagh, Northern Ireland, Britain November 7, 2019.

• Boris Johnson just accidentally made the perfect argument for remaining in the EU.
• Speaking in Northern Ireland, Johnson said his Brexit deal would allow the province to keep free movement and access to the Single Market and described this as a "great deal"
• However, these benefits will both be lost by the rest of the United Kingdon.
• This provokes the obvious question as to why his deal denies this to the rest of the UK.
• Visit Business Insider's homepage for more stories.

LONDON - Prime Minister Boris Johnson made an unusual and very revealing comment on Thursday night which accidentally makes an incredibly compelling argument against his own Brexit deal.

Speaking at a meeting of local Conservatives in Northern Ireland on Thursday evening, the prime minister said: "Actually, Northern Ireland has got a great deal. You keep free movement, you keep access to the single market, but you also, as it says in the deal, have unfettered access to [Great Britain]."

This poses a rather obvious question.

If retaining free movement and staying in the single market is such a "great deal" for Northern Ireland, then why has Johnson prioritised a Brexit plan which ensures the rest of the UK is prevented from having that same access and freedom?

As the Liberal Democrat MP Tom Brake pointed out this morning: "The Single Market and freedom of movement are a great deal  - even Boris Johnson recognises this - so why isn't he keeping them for the whole of the UK as part of the many benefits of EU membership?

Watch Boris Johnson argue against his own Brexit deal

The Brexit deal Johnson brokered with the EU in October would see the UK leave both the single market and customs union, as well as ending free movement and replacing it with a "points-based" immigration system similar to Australia's.

The prime minister insists this deal will see the UK "taking back control of our money, our laws, and our borders."

However, analysis by the National Institute of Economic and Social Research suggests it would make every person in the UK £1,100 poorer a year on average. The independent forecaster found the prime minister's withdrawal plan would leave the UK £70 billion worse off a year and shave nearly 4% off the economy by the end of the 2020s.

Most of that lost output is directly caused by barriers to trade that arise from the UK's decision to leave the single market and customs union, which is exactly why Johnson appears to be arguing that Northern Ireland's exemption from this is so beneficial.

His comments are also a gift to the Scottish National Party.

SNP leader and Scottish First Minister Nicola Sturgeon, whose party is launching its own election campaign on Friday, will now surely argue that if staying close to the EU is such a "great deal" for Northern Ireland, then why can't all the other nations of the UK be given this deal too.

Our Brexit Insider Facebook group is the best place for up-to-date news and analysis about Britain's departure from the EU, direct from Business Insider's political reporters. Join here.