Theresa May has received fresh backing for her Brexit deal - but still faces a fraught battle to win enough support for her withdrawal agreement ahead of an EU summit this week.
In a significant boost for the prime minister, former Conservative chancellor Lord Lamont and ex-Northern Ireland first minister Lord Trimble have both argued there are reasons to support her deal, despite their previous objections.
Speaking ahead of a meeting of EU foreign ministers on Monday, Foreign Secretary Jeremy Hunt said new support for the prime minister's deal had given the government "cautious signs of encouragement".
However, some opponents to Mrs May's deal, such as former foreign secretary Boris Johnson, repeated their opposition to her agreement and urged her to go back to the EU again to try to win further concessions.
The prime minister has said, if MPs approve her deal by Wednesday, she will head to a Brussels summit on Thursday to ask for a three-month delay to Brexit to give parliament time to pass necessary legislation.
However, if MPs continue to decline to back her withdrawal agreement this week, she has said a much longer delay to Brexit is likely, which could also see the UK take part in EU elections in May.
Downing Street has said there must be a "realistic prospect" of success for the prime minister's deal, before a third "meaningful" vote on her withdrawal agreement is held in the Commons.
Lord Lamont, a prominent eurosceptic, used an article in the Daily Mail to warn the opportunity to leave the EU "will never happen again and history will not understand if it is Conservative MPs who prevent us reclaiming our self government".
He claimed delay to the UK's departure from the EU of a year or more would see Brexit as "truly dead", with the mandate from the 2016 referendum diminishing further.
"If the PM's deal is rejected by the House of Commons, we may not leave the EU for many months and possibly not all," Lord Lamont wrote.
Meanwhile, Lord Trimble, a former leader of the Ulster Unionist Party who now sits as a Conservative peer in the House of Lords, has co-authored a new report that argues the potential impact of the Irish border backstop arrangement has "significantly changed in the course of recent negotiations".
Lord Trimble previously took the government to court to claim the backstop - an insurance policy to avoid a hard border on the island of Ireland if talks on a future EU-UK trade relationship break down - is in breach of the Good Friday Agreement and should be removed from Mrs May's Brexit deal.
But, in a research note for the Policy Exchange think tank, he argued that, in recent weeks, the government "has succeeded in securing substantive changes that will affect and limit the impact of the Irish backstop, if it is ever put in place".
Although neither Lord Lamont or Lord Trimble will vote in the Commons on Mrs May's deal, their opinion could prove significant in persuading Brexiteer MPs to finally back the prime minister.
Prominent Brexiteer Jacob Rees-Mogg, the chair of the European Research Group (ERG) of Tory eurosceptics, also signalled he could now drop his opposition to the prime minister's deal.
He told LBC Radio on Monday: "No deal is better than a bad deal, but a bad deal is better than remaining in the EU."
However, Mr Rees-Mogg said he would continue to oppose the deal if the DUP, who are engaged in discussions with the government over the backstop, also fail to find a reason to support it.
Yet, Mr Johnson is holding firm in his opposition, using his weekly Daily Telegraph column to demand the prime minister use this week's EU summit to "get real change to the backstop".
Twenty-three Tory MPs also penned a letter in the Daily Telegraph to suggest they will maintain their "no" vote against the Brexit deal, despite the prospect of a long delay to leaving the EU.
They wrote: "It is not our fault that we are confronted by two unacceptable choices, but it will be our fault if we cast a positive vote in favour of either for fear of the other."
Despite a third Commons vote on Mrs May's withdrawal agreement being expected this week, Chancellor Philip Hammond and International Trade Secretary Liam Fox - along with Downing Street - have since said the government will only go ahead if they are confident of winning.
The prime minister's deal has already been twice rejected by an overwhelming majority of MPs.
Over the weekend, former Tory cabinet minister Esther McVey - who quit the government in protest at Mrs May's Brexit strategy - told Sky News that Brexiteers like her would have to surrender "purity" in order to prevent Brexit being stopped altogether.
Matthew Elliott, the boss of the Vote Leave campaign during the EU referendum, has also told MPs to "see the grave risks" of voting down the prime minister's deal again and to support the agreement.
However, former Brexit secretary David Davis, who resigned in protest against the deal but then voted for it last week, has said he could change his mind once again.
Labour MP Peter Kyle told Sky News on Monday he has received "broad support" from party leader Jeremy Corbyn for his plan to hold a "confirmatory" referendum, in which the public will be asked to choose between the prime minister's deal or cancelling Brexit.
He will push his proposal via a Commons amendment when Mrs May's agreement is voted on again by MPs.