British Prime Minister Theresa May talks with a caseworker and domestic violence survivor at Advance Charity offices in West London, May 13, 2019. (Photo: CGTN)

British Prime Minister Theresa May was under pressure from her own party on Tuesday to abandon a bid to find a Brexit compromise with the opposition Labour Party.

Nearly three years since the United Kingdom voted 52% to 48% to leave the European Union (EU), there is still no agreement among British politicians about when, how or even if the divorce should take place.

It was due to have left the European Union on March 29, May has been unable to get her divorce deal approved by parliament so she has turned to the Labour Party, led by socialist Jeremy Corbyn, in a bid to court his support.

Thirteen of May's former cabinet colleagues as well as Graham Brady, chairman of the 1922 Committee of Conservative lawmakers, wrote to May to ask her not to agree Labour's demand for a post-Brexit customs union with the EU.

"You would have lost the loyal middle of the Conservative Party, split our party and with likely nothing to show for it," the letter said. "We urge you to think again."

"No leader can bind his or her successor so the deal would likely be at best temporary, at worst illusory," said the letter which was signed by Gavin Williamson, who was sacked as defense secretary earlier this month, and former foreign minister Boris Johnson.

Labour Party leader Corbyn said last week that May had made no big offer on Brexit and had not moved her "red lines".

May's chief Brexit negotiator, Olly Robbins, is due in Brussels to discuss changes to the political declaration on the UK's future relationship with the EU.