British Prime Minister Theresa May reopened talks with the European Union leaders on the Brexit agreement on Thursday and was bracing for a clash with senior EU officials during a day of divorce negotiations.

European Commission President Jean-Claude Juncker shakes hands with British Prime Minister Theresa May before their meeting at the European Commission headquarters in Brussels, Thursday, Feb. 7, 2019. [Photo: AP]

May was welcomed by European Commission Jean-Claude President Juncker in a glum, stiff handshake ceremony that underscored the simmering tension between the U.K. and the other 27 EU member states.

With the planned departure date of March 29 closing in, May is expected to be stonewalled by the EU officials when it comes to reopening the legal withdrawal agreement which was already endorsed in November before the U.K. Parliament overwhelmingly rejected it.

The gap between both sides was already yawning, but European Council President Donald Tusk exacerbated the frosty climate on Wednesday by wondering aloud what "special place in hell" might be reserved for those who backed Brexit while having no idea of how to deliver it.

Highlighting the sensitivities, a public welcome appearance on camera between May and Tusk was suddenly cancelled, hours before the encounter.

And instead of jovial kisses, as is often his wont, Juncker held out his hand for May to shake and quickly ushered her off into his offices, with one reporter shouting at her "Is this hell, prime minister?"

U.K. officials said May's primary concern was not to be "trapped" into a controversial system to avoid lengthy checks on the Irish border which could see Britain linked to the EU in a customs union for an indefinite time.

Britain's Parliament voted down May's Brexit deal last month, largely because of concerns about a provision for the border between the U.K.'s Northern Ireland and EU member Ireland. The mechanism, known as the backstop, is a safeguard that would keep the U.K. in a customs union with the EU to remove the need for checks along the Irish border until a permanent new trading relationship is in place.

Many pro-Brexit British lawmakers fear the backstop will trap Britain in regulatory lockstep with the EU, and say they won't vote for the withdrawal agreement unless it is removed.

May will still be looking for changes in the 585-page legally-binding withdrawal agreement, something which the 27 other EU leaders continue to vehemently oppose.

May insists that "alternative arrangements" can be found, but EU officials have been waiting for weeks for London to spell out what they are.

In London, there was significant momentum from the opposition with the Labour Party making perhaps its biggest move in months.

Party leader Jeremy Corbyn dangled a possible way out of the impasse, saying his left-wing party could support a Brexit deal if May committed to seeking a close relationship with the EU after Britain leaves, including a commitment to maintain roughly equivalent standards in areas such as the environment and workers' rights.

Corbyn's key demand, set out in a letter to May, is permanent British membership in a customs union with the EU. May has repeatedly ruled that out, but it would solve the problem of the backstop, by making customs checks on the Irish border unnecessary.

It is the firmest signal yet that Labour lawmakers might be willing to vote for a Brexit deal in Parliament. But the party — like May's Conservatives — is divided. Corbyn's position disappointed some Labour Party legislators who had hoped he would back calls for a second referendum on whether to leave the EU.