A final Brexit deal is now “within our grasp,” Theresa May has confidently declared, following a breakthrough agreement on Britain’s future relationship with the European Union.

Speaking outside 10 Downing Street after briefing Cabinet colleagues, the Prime Minister said a political declaration on post-Brexit relations agreed with Brussels was "the right plan for the UK," which would set the country on course for a brighter future.

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But her opponents denounced the 26-page future framework document as full of vague aspirations.

Nicola Sturgeon, the First Minister, dismissed the text as "lots of unicorns taking the place of facts about the future relationship".

Labour’s Chukka Umunna, a leading Remainer, was also critical, saying the text amounted to a “blindfold Brexit,” that promised nothing but “years of uncertainty”.

Another opponent of Brexit, Conservative MP Philip Lee, who quit the Government in protest at its handling of the withdrawal process, said it "reads like a letter to Santa".

The political declaration also found no favour among Brexiteers.

Leave-backing Tory MP Marcus Fysh said the political declaration made Mrs May's withdrawal agreement "even more toxic".

Mark Francois, a leading figure in the pro-Brexit Tory European Research Group, stressed how the political agreement was not binding under any international law.

“It is 26 pages of political camouflage designed to take people's eye off the withdrawal agreement and try and persuade them to vote it through. It will not work," he declared.

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"The legally binding element in this is the withdrawal agreement. That is what MPs will vote on in the meaningful vote. This is a fig leaf. Even with this, which won't fool anybody, they will never get the withdrawal agreement through the House of Commons," added the Tory backbencher.

Meanwhile, Labour’s Lesley Laird, the Shadow Scottish Secretary, picked up on the document’s section on fishing, which pointed to a future agreement by July 2020, and said Scottish Tories, who had raised fears over the UK’s future control of its own waters, would not be able to accept the text and called on David Mundell, the Scottish Secretary, to resign.

But Andrew Bowie, the Conservative MP for West Aberdeenshire and Kincardine, was effusive in his welcome for the “unique agreement,” saying it helped secure a smooth and orderly exit from the EU.

“This deal delivers on the result of the 2016 referendum. It gives the UK control over our borders, it protects jobs, it gets us out of the Common Fisheries Policy, the Common Agricultural Policy and guarantees the rights of EU citizens living here and UK citizens abroad.”

He called on all MPs from all parties to get behind it and act in the national interest, adding: “We must get behind the Prime Minister and ensure we can move on to the next stage of crucial talks on future trading arrangements.”

Mrs May, who held talks with Jean-Claude Juncker, the European Commission President, in Brussels yesterday evening, said following it officials had been tasked with working through the night to come up with a new document, which they had and which had now got the political agreement of both sides.

The breakthrough clears the way for the special summit in Brussels on Sunday, at which leaders of the remaining 27 EU states are expected to give their stamp of approval to both the future framework and a separate withdrawal agreement setting out the terms of the UK's departure.

The PM, who will make a Commons statement this afternoon, said: “This is the right deal for the UK. It delivers on the vote of the referendum, it brings back control of our borders, our money and our laws and it does so while protecting jobs, protecting our security and protecting the integrity of the United Kingdom."

Confirming that she would return to Brussels on Saturday for further talks with Mr Juncker ahead of the summit, she added: "The British people want this to be settled, they want a good deal that sets us on course for a brighter future. That deal is within our grasp and I am determined to deliver on it."

Agreement on the text was announced by Donald Tusk, the European Council President, who said in a tweet: "I have just sent to EU27 a draft Political Declaration on the Future Relationship between EU and UK.

"The Commission President has informed me that it has been agreed at negotiators' level and agreed in principle at political level, subject to the endorsement of the leaders."

Downing Street has always stressed that the 585-page legally binding withdrawal agreement setting out the terms of the UK's departure from the EU - including a "divorce bill" estimated at £39 billion - can only be finalised alongside the shorter declaration setting out the two sides' aspirations for their future relations.

Mrs May will hope that the prospect of an ambitious free trade deal set out in the 26-page declaration will win over some of the Conservative MPs who have voiced deep misgivings about her plans. The focus at Westminster will now begin to move towards next month’s “meaningful vote”.

The new text calls for an "ambitious, broad, deep and flexible partnership" covering trade, law enforcement, foreign policy, security and defence, which could take the form of a Ukraine-style Association Agreement.

It confirms that the future relationship must respect the sovereignty of the UK and its right to develop an independent trade policy and end the free movement of EU nationals.

And it leaves open the possibility of using technological solutions to keep the Irish border open after Brexit.

But other elements of the declaration could anger Brexiteers, including:

*plans for a "free trade area, combining deep regulatory and customs co-operation", building and improving on the "single customs territory" provided for in the withdrawal agreement;

*a commitment to "work together" on safeguarding workers' rights and consumer and environmental protections;

*provisions to ensure a "level playing field" on business competition, which could cover areas including state aid, climate change laws and tax and

*a role for the European Court of Justice in providing "binding" rulings on the interpretation of EU law in any disputes between the two sides.

The document envisages negotiations beginning immediately after the formal date of Brexit on March 29 2019 with high-level conferences every six months.

Agreements on "equivalence" of financial services regulations and access and quotas for fishing should be reached in time to come into effect at the end of the transition period on December 31 2020.