LONDON, Dec. 14 (Xinhua) -- British Prime Minister Theresa May returned almost empty handed from Brussels Friday, knowing that on Monday she faces trying to convince MPs at Westminster that her under-fire Brexit deal can still succeed.

With just over 100 days to go before Britain ends its 46 year membership of the European Union (EU), a future UK-EU trading relationship is far from winning the green light.

NO GUARANTEES ON BACKSTOP

May returned to 10 Downing Street Friday night after a so-called charm offensive to win more support for the Brexit deal she has brokered with the EU.

Her reassuring words delivered at a press conference in Belgian capital failed to win over critical MPs at Westminster, with concerns that the EU has insisted that the Irish border safety net proposals, known as the backstop, must remain as part of the deal.

May was unable to win any cast-iron guarantees that the backstop would never be applied.

Both sides agreed that efforts will be made in a near two-year implementation period to reach a permanent future trade deal.

If that fails, the EU has said even for a temporary period, Northern Ireland would have to follow EU rules rather than build a hard border with the neighboring Irish Republic.

The Democratic Union Party (DUP) which helps give May's minority government at Westminster its slender majority, has insisted it will not accept a backstop. Their main concern is that it would mean different rules are applying in Northern Ireland than in the rest of the British mainland.

In Brussels Friday, May said the EU had made it clear it is their firm determination to work speedily on a future relationship or alternative arrangements which ensure there is no hard border by Dec. 31, 2020 so the backstop will not need to be triggered.

May added the EU stands ready to embark on preparations so that negotiations on the future partnership can start as soon as possible. She added that as the conclusions were formal, the EU commitments have legal status and therefore should be welcomed.

"There is work still to do and we will be holding talks in coming days about how to obtain the further assurances that the UK Parliament needs in order to be able to approve the deal," said May.

CALL FOR BREXIT DEAL VOTE

The main opposition Labour Party will press May in the House of Commons on Monday to give MPs a meaningful vote on her Brexit deal before Christmas. That would mean a vote before Thursday, with MPs heading home afterwards for the Christmas and New Year holiday.

With politicians returning to Westminster on Jan. 7, May has promised a vote on the deal before a crucial deadline of Jan. 21.

Labour Party poured cold water on what May had achieved during two days of talks with EU leaders and European heads of state.

Labour leader Jeremy Corbyn said: "The last twenty four hours have confirmed that Theresa May's Brexit deal is dead in the water."

Corbyn said the prime minister had utterly failed in her attempts to deliver any meaningful changes to her botched deal.

He added: "Rather than ploughing ahead and dangerously running down the clock, the Prime Minister needs to put her deal to a vote next week so Parliament can take back control."

Tom Brake, Brexit spokesman for the minority Liberal Democrats, said: "Having watched the Prime Minister's botched attempt to negotiate with EU leaders, people up and down the country will be more concerned by Brexit than ever before."

A 2ND REFERENDUM? AND POLITICAL STORM?

Meanwhile, former British prime minister Tony Blair, a strong supporter of Britain remaining in the EU, said in a speech Friday there would soon be a majority in the British parliament for a second referendum on EU membership.

Addressing a meeting at the Royal Academy in London, organised by the People's Vote Campaign, Blair said: "What has been revealed by the whole negotiation process is that all the Brexit options have significant drawbacks compared with staying in the EU. This pursuit of incompatible ends through inept means has led us to the present impasse."

Blair told the meeting: "My advice to her (May) is there's no point literally in carrying on banging your head against this brick wall. It's sensible to take your head off the brick wall and think creatively."

May survived a confidence vote among Conservative MPs this week by a vote of 200 to 117, but a second political storm could lie ahead.

Keir Starmer, chief Brexit spokesman for the Labour Party, said in media interviews Friday it was clear the Prime Minister would not secure any meaningful changes to her deal and that she should face the music and put her deal to a vote next week.

Starmer said on Sky News that confidence in May was "seeping away on all sides" and "it is a question of when, not if" the Labour Party will table a vote of no confidence in the Conservative government.