Britain's Prime Minister Theresa May leaves 10 Downing Street in London on February 5, 2019. - A top EU official warned Monday that the prospect of Britain crashing out of the bloc next month looks more likely than ever, as Prime Minister Theresa May sought to reassure foreign investors worried about a chaotic Brexit.

U.K. Prime Minister Theresa May is in Brussels on Thursday seeking changes to the Brexit deal with the European Union (EU) with just 50 days to go until the Brexit departure date.

May met European Commission President Jean-Claude Juncker Thursday morning and the pair said they would work together to "achieve the U.K.'s orderly withdrawal from the EU." In a joint statement issued after their meeting, Juncker said EU would not reopen negotiations over the Brexit deal reach with the U.K. (known formally as the "Withdrawal Agreement").

However, he said he was open to adding wording to the "Political Declaration" agreed by the EU and the U.K. (which sets out the terms of a future relationship and guidelines for future trade talks) to make it "more ambitious in terms of content and speed when it comes to the future relationship between the European Union and the UK."

May had gone to Brussels to seek changes to the Brexit deal, however, and especially the thorny subject of the Irish "backstop" within it. The backstop is something of an insurance policy designed to prevent a hard border between the Republic of Ireland and Northern Ireland if there's no trade deal between the U.K. and EU.

May sought changes to the backstop arrangement within the Brexit deal (known formally as the "Withdrawal Agreement") because of widespread objection to it in the U.K. Parliament.

She headed for the continent ready to tell her European counterparts Thursday that the U.K. "cannot, and will not, be trapped in the backstop," according to remarks released earlier by Downing Street. The U.K. is exploring "alternative arrangements" and legal provisions to the current backstop, the statement said.

The EU has said repeatedly that it will not renegotiate the withdrawal agreement, however. Speaking on Wednesday, European Council President Donald Tusk said the EU would "insist" on the backstop.