Theresa May issued a direct plea to the public to support her Brexit deal as European Union leaders prepared to endorse the package.
The Prime Minister will meet the other 27 EU leaders in Brussels after they have given their backing to the Withdrawal Agreement and Political Declaration thrashed out by negotiators.
In a "letter to the nation", Mrs May said leaving the EU on March 29 2019 would mark "a new chapter in our national life" and there would be a moment of "renewal and reconciliation" after the bitter battles over Europe.
EU chief negotiator Michel Barnier said "now it is time for everybody to take their responsibility" as leaders arrived in Brussels to consider Mrs May's Brexit deal.
Pressed about whether the EU is open to renegotiation, President of the European Commission Jean-Claude Juncker said: "This is the deal.
"It's the best deal possible and the EU will not change its fundamental position when it comes to these issues".
- What does the letter say?
The almost 800-word message is an attempt to speak directly to the public to build support for her deal, which faces widespread opposition at Westminster including from both wings of her Conservative Party and the Democratic Unionist Party which props up her administration.
Mrs May said the deal "will honour the result of the referendum" by allowing the UK to "take back control" of its money, laws and borders.
"It is a deal for a brighter future, which enables us to seize the opportunities that lie ahead," she said.
She promised she would be "campaigning with my heart and soul" to win the vote in the Commons.
The summit in Brussels is only taking place after Spain claimed the UK and EU had given into its demands for concessions over the future of Gibraltar.
Spanish Prime Minister Pedro Sanchez claimed the UK and European Union had agreed to its demands for guarantees over the status of Gibraltar in future negotiations.
Madrid's foreign minister Josep Borrell went further, saying the agreement is "highly positive for Spain" and "the most important" since the Treaty of Utrecht in 1713 under which Gibraltar was ceded to the UK.
But Mrs May told reporters in Brussels: "The UK's position on the sovereignty of Gibraltar has not changed and will not change.
"I am proud that Gibraltar is British and I will always stand by Gibraltar."
- What's been the response?
It has provoked impassioned responses from those on both sides of the debate.
Scotland's First Minister hit out at Theresa May's public message saying "almost nothing in this desperate letter is true".
Minister for Sport, Civil Society and Loneliness Mims Davies, a Conservative, backed Mrs May, saying it was “time to unite & progress”.
She tweeted: “@theresa_may has written to us ALL.I believe like PM its time for us all to be ready to listen & all move forward.Lets not just re fight referendum forever more, lets not focus on a divide,use incendiary language,argue more than we look for common ground.”
Welsh Labour MP Stephen Doughty, supporter of the People’s Vote campaign, fired off a quick reply to the PM.
“Not thanks. Not buying it,” it said.
“Let’s have a People’s Vote instead to let the people of this country have a final say, with the option to stay.”
Tory MP Sarah Wollaston, chairwoman of the Commons Health Select Committee, rejected the PM’s assertion that hers is “a deal for a brighter future”.
“Not a brighter future, just dimmer & diminished. There is no valid consent to this Deal without a #PeoplesVote,” she tweeted.
Scottish Labour MP Ged Killen likened Mrs May’s pledge to end free movement of people “once and for all” to comments US president Donald Trump might make.
He tweeted: “Feels like something Trump might tweet. Still breaks my heart to think my nieces and nephews won’t grow up with the same freedom I had to live, work and study across the EU”
- What happens now?
If the EU approves Mrs May's deal she will then need to get Parliament to back it.
However, the DUP, Labour, SNP and the Liberal Democrats have said they will vote against it in December.
If the withdrawal agreement is rejected by MPs it could mean a general election or the UK leaving with no deal unless Mrs May attempts to renegotiates another deal.
The Prime Minister's political difficulties at home show no sign of abating, with speculation that Remain-leaning Cabinet ministers have begun secret talks on a Brexit "Plan B" if the deal is rejected by MPs.
The Sunday Times reported that Chancellor Philip Hammond - who warned on Saturday of "economic chaos" if there is no deal - is working with David Lidington, Amber Rudd, Greg Clark and David Gauke on trying to persuade Mrs May to adopt a softer Brexit which may be able to get through Parliament if her plan is rejected.
The Sunday Telegraph also reported that "several senior ministers" were working on plans for a Norway-style relationship with the EU.