- What exactly is being proposed?
He insisted that the government remained committed to the principles of the deal, which will see customs checks on some goods moving from the rest of the U.K.to Northern Ireland.
"We will always reserve the right to act in the best interests of Northern Ireland and the UK's internal market", she said.
The divorce deal allowed for a transition period through to the end of this year, during which the two sides are meant to sort out a trade agreement for the future.
Britain formally left the 27-member bloc on January 31 but remains bound by European Union rules until the end of December while it tries to thrash out new terms of its relationship.
The Prime Minister's official spokesman said the Government was proposing "limited clarifications" to the law to ensure ministers can preserve the gains of the Good Friday Agreement in the event of no deal.
Meanwhile, the Daily Mail leads on its own campaign to "get Britain flying again", and Priti Patel's vow to take a sterner stance against Extinction Rebellion protesters.
But Mr Johnson, in an apparent bid to focus minds as another set of talks gets under way on Tuesday, will say that there is "still an agreement to be had", one that is based on deals Brussels has previously struck with "Canada and so many others".
Frost, who was appointed to his position in January, said the United Kingdom will not accept being a "client state".
Negotiations by the Joint Committee take place between Chancellor of the Duchy of Lancaster Michael Gove, and EU Commission Vice President, Maroš Šefčovič.
Turning up the pressure on the EU, Prime Minister Boris Johnson is threatening to table new legislation and override requirements for new Northern Ireland customs arrangements, meant to prevent the return of checks at the Irish border from next year.
Both sides have said a deal would need to be done by mid-October in order for it to be ratified in time.
The announcement triggered a backlash from governments around Europe as accusations of bad faith negotiating were flung at Mr Johnson.
According to Johnson, if the two sides don't agree by 15 October there will be no free trade agreement, and they "should both accept that and move on".
President of the European Commission Ursula von der Leyen tweeted: "I trust the British government to implement the Withdrawal Agreement, an obligation under worldwide law & prerequisite for any future partnership".
Irish foreign minister Simon Coveney said the reported development would be "a very unwise way to proceed".
Although the European Union made avoiding a hard border on the island of Ireland a key priority in its Brexit negotiating strategy, threatening to tear up the Irish Protocol is a risky move domestically for Johnson.
- How is the UK Government presenting the situation?
Asked about the report in the Financial Times, British Environment Secretary George Eustice said there might be some minor "legal ambiguities" that needed to be tidied up over the Northern Irish protocol.
"We are now entering the final stages of our negotiations with the EU", Mr Johnson is expected to say.
However, the devil is in the detail as the matter is fraught with multiple political and technical challenges.