THERESA May has received a boost to her flagging Brexit plan after European Council President Donald Tusk recommended the EU approve the draft deal at a summit which will be staged today.

Spain was believed to be considering boycotting the crunch talks amid concerns over Gibraltar, but Spanish Prime Minister Pedro Sanchez said he had received the written guarantees he needed over Spain's role in the future of the British territory.

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.

Tusk’s comments now pave the way for members of the EU to back a deal which all sides believe has its flaws.

However, May’s plan still faces fierce resistance at Westminster, with many of her own MPs believing the Northern Ireland “backstop” could leave the UK trapped in the EU after Brexit.

At yesterday’s conference of Northern Ireland’s pro-Brexit Democratic Unionist Party, which helps keep the Tories in office, senior DUP and Conservative figures lined up to denounce the draft plan.

A key problem in the UK/EU talks has been avoiding a hard border between Northern Ireland and the Republic after the transition period ends in 2020.

Two options are contained in the draft: extending the period of transition; or moving to a backstop which keeps the UK in a customs arrangement with the rest of the EU.

According to the draft, the UK could not independently leave the backstop, which has infuriated the DUP and pro-Brexit Tories. For the plan to be accepted, May has to receive the support of the EU member states and the UK Parliament.

Tusk, a key player in the negotiations, yesterday released a statement which recommended the EU states approve the deal:

“I believe that we have finally found the best possible compromise. Given all of the above, I will recommend that on Sunday we approve the outcome of the Brexit negotiations.”

He added: “And although no-one will have reasons to be happy on that day, there is one thing I would like to stress: at this critical time, the EU27 has passed the test of unity and solidarity.”

However, the speeches at the DUP conference showed how hard it will be for the Prime Minister to secure the support of a majority of MPs.

DUP deputy leader Nigel Dodds told the Prime Minister: "In the coming weeks Parliament will be faced with a clear choice on the future of our country.

"To be a free independent trading nation leaving the EU as one United Kingdom or to be locked into an EU straitjacket, divided and diminished.

"The published Withdrawal Agreement portrays a pitiful and pathetic place for the United Kingdom.

"Hundreds of pages are devoted to a backstop which will bind the United Kingdom into taking the rules of the EU with no right to leave and no end date."

Also addressing the Belfast conference, former foreign secretary Boris Johnson helped the Prime Minister by urging the DUP to stick with their power sharing deal with the Conservatives.

However, the leading Brexiteer resumed his attacks on the draft by saying the UK was on the verge of "making a historic mistake".

"If we are not careful, we are going to stay in the customs union, we are going to stay in the single market, we are going to be rules takers," he said.

"Unless we junk this backstop, we will find that Brussels has got us exactly where they want us - a satellite state.

Meanwhile, the Prime Minister has written a “letter to the nation”, insisting her EU withdrawal agreement will work "for our whole country and all of our people,

whether you voted 'Leave' or 'Remain"'.

She wrote: “We will take back control of our borders, by putting an end to the free movement of people once and for all. Instead of an immigration system based on where a person comes from, we will build one based on the skills and talents a person has to offer. We will take back control of our money, by putting an end to vast annual payments to the EU.

"Instead, we will be able to spend British taxpayers' money on our own priorities, like the extra £394 million per week that we are investing in our long-term plan for the NHS."

In another development, First Minister Nicola Sturgeon challenged May to a debate on the Brexit proposals.

Amid speculation that the Prime Minister could hold a debate with Labour leader Jeremy Corbyn before MPs vote on the deal, Sturgeon tweeted: "I can't speak for @jeremycorbyn, but I'd be up for a full leaders debate on the 'deal'. So, how about it PM @theresa_may?"