Video report by ITV News Political Editor Robert Peston
A Brexit deal between the UK and EU has been agreed on a "technical level".
Negotiators came to an accord in Brussels on Tuesday.
The proposed agreement is set to be scrutinised at a special Cabinet meeting on Wednesday.
There, Theresa May will hope that she can secure support for the deal from ministers.
Downing Street confirmed that a deal had been struck shortly after reports began circulating.
Within the agreement was a "stable" text on the thorny issue of the Northern Irish border, according to broadcaster RTE.
RTE said the deal involved one overall backstop in the form of a UK-wide customs arrangement, but with deeper provisions for Northern Ireland on customs and regulations.
A Downing Street spokesperson said in a statement: "Cabinet will meet at 2pm tomorrow to consider the draft agreement the negotiating teams have reached in Brussels, and to decide on next steps.
"Cabinet ministers have been invited to read documentation ahead of that meeting.
A spokesman for chief EU negotiator Michel Barnier said the latest in the negotiations had been set out earlier by commission vice president Frans Timmermans who said that while the talks were making progress "we are not there yet".
"The UK cabinet will meet tomorrow. We will take stock at the midday presser," the spokesperson said.
Responding to reports of a deal being agreed, the Irish Government said that "nothing has been confirmed".
A spokesperson said: "We're at a stage where there is still no agreement at this point in time.
"There is actually no agreement."
A spokesperson for Ireland's deputy premier Simon Coveney also called for caution.
"Negotiations between the EU and UK on a Withdrawal Agreement are ongoing and have not concluded," they said.
Ex-Ukip leader Nigel Farage told ITV News he believes the prime minister has a "60-40" chance of getting her deal through the Cabinet.
"The moment of truth is here," Mr Farage said.
"Are we going to see Cabinet resignations? Are we going to see people in the House of Commons wholesale saying this is not what the referendum is about.
"History tells us that, however much speculation there is, generally politicians don't like resigning nice jobs."
He added: "History tells me, however awful this deal is, she [Theresa May] will probably get it through."
Brexiters Boris Johnson and Jacob Rees-Mogg were also quick to state they would vote down the deal in Parliament.
Ex-mayor of London Mr Johnson told ITV News the deal was "vassal state stuff" and urged the Cabinet to "chuck it out".
"From what I've seen it's about as bad as it possibly could be," he said.
"What we seem to be on the verge of agreeing, and I devoutly hope that we don't, is not only that the whole of the UK remains in the customs union... but you are also going to have effectively a border for customs checks and regulatory checks down the Irish sea."
Tory MP Mr Rees-Mogg described the deal as a "betrayal" of the UK and the Conservative Party manifesto - leaving the country tied to the customs union and single market.
"Everything one knows about it so far makes it sound not only a bad deal but an abject surrender," MR Rees-Mogg told ITV News.
The DUP, upon who the Government rely, repeated their warning that they would not accept any deal which places new trade barriers between Northern Ireland and the Republic of Ireland.
DUP leader Arlene Foster said: "Over time, such a deal will weaken the Union. No unionist Prime Minister could argue that such a deal is in the national interest.
"It would be democratically unacceptable for Northern Ireland trade rules to be set by Brussels. Northern Ireland would have no representation in Brussels and would be dependent on a Dublin government speaking up for our core industries."
She added: "I am heartened by friends of the Union on both sides of the House and across the United Kingdom who have pledged to stand with the DUP in opposing a deal which weakens the Union and hands control to Brussels rather than Parliament."
Labour's shadow Brexit secretary Sir Keir Starmer warned Mrs May that the deal would have to pass the party's "conditions and tests".
"Given the shambolic nature of the negotiations this is unlikely to be a good deal for Britain," Sir Keir said.
"We'll look at the detail but we've been very clear that if it doesn't meet our conditions and tests then we will voting against it."
Party leader Jeremy Corbyn said: "Labour has been clear from the beginning that we need a deal to support jobs and the economy - and that guarantees standards and protections.
"If this deal doesn't meet our six tests and work for the whole country, then we will vote against it"
Labour MP David Lammy warned that MPs would soon face a choice between "their jobs and the country" when it came to a Parliamentary vote.
He tweeted: "Tonight cabinet members will go into Number 10 one by one. Each will have the choice to put their country before their jobs and support a #PeoplesVote.
"Soon every MP will face a similar decision in Parliament. History will judge the makers of Brexit harshly."
Liberal Democrat leader Sir Vince Cable warned the prime minister would not be able to get the agreement through Parliament and called for a second referendum as "the only way to escape from this mess".
"Any Brexit deal will leave the UK weakened and the public poorer. Before the ink is dry, the Conservative Party will tear into what little Theresa May has been able to agree," he said.
"The Prime Minister now faces a defeat in Parliament, as a majority will be hard or impossible to secure for what she has come up with."
Scotland first minister Nicola Sturgeon said on Twitter: "If the PM's 'deal' satisfies no-one and can't command a majority, we mustn't fall for her spin that the UK crashing out of EU without a deal is then inevitable - instead we should take the opportunity to get better options back on the table."