Boris Johnson wants to scrap the Irish backstop – the insurance policy designed to prevent a hard border.
The Prime Minister is proposing that from 2021 Northern Ireland and the Irish Republic share the same EU single market rules.
This removes the need for checks on livestock and some goods at the Irish border.
But this would require a border in the Irish Sea to monitor food and animal products entering Northern Ireland from mainland Britain.
And officials on both sides of the English Channel said on Wednesday morning numerous obstacles still needed to be surmounted for a fresh agreement to be brokered.
The PM updated his cabinet members about the progress of the deal before EU chief negotiator Michelle Barnier briefed ambassadors at 6pm.
Mr Johnson laid out his proposals to the 1922 Committee, who are likely to be crucial in determining whether the bill passes through Parliment.
Why is it so controversial?
The talks hit two major stumbling blocks: customs and consent.
The DUP has previously objected to a border in the Irish Sea as it fears it could lead to Northern Ireland’s annexation from the UK.
There is an issue with Northern Ireland having to follow EU single market rules without any say.
The PM proposed the system would face rolling consent with the Northern Irish Assembly or a review by the executive every four years.
Are there any other problems?
Plenty. For a start the UK and the Irish Republic have different VAT rates and, after we leave the EU, will charge different tariffs on goods.
A system will have to be put in place to tax goods exported from Britain to Eire via Northern Ireland.
Mr Johnson’s plan is also a much harder Brexit than Theresa May ’s.
GDP per capita would fall by up to 7% in 10 years, says the UK in a Changing Europe think tank. There is no guarantee on workers’ rights or environmental safeguards.
Can he get it through the Commons?
The numbers are tight. He needs the support of all 288 Conservative MPs, the 21 Tory MPs who’ve lost the Whip, all 10 DUP MPs and at least one Labour or independent. That takes him to the magic 320 needed for a majority.
Does this mean Brexit is sorted by October 31?
Far fro, it. The UK and EU parliaments must approve a deal.
Opposition MPs in the Commons will try to amend the legislation, with the Lib Dems saying they will push for a second referendum.
If a deal is passed the UK still has to hammer out a trade deal with the EU which will be more tortuous.
We have to strike agreements with the EU on intelligence sharing, security and data transfers, and agree dozens of trade deals with countries such as the US and China.
