Theresa May leaves 10 Downing Street in London on Wednesday. Tolga Akmen / AFP

British Prime Minister Theresa May's final Brexit gambit was in tatters on Wednesday as lawmakers in her own party rejected a compromise offer and called for her to resign immediately.

Nearly three years since Britain voted 52% to 48% to leave the European Union, the beleaguered May made one last pitch on Tuesday to get her divorce deal approved by the British parliament before her crisis-riven premiership ends.

She offered a parliamentary vote on whether to hold a second Brexit referendum - once her legislation passes the first stage - as well as closer trading arrangements with the EU in future as incentives to what she called the only way to prevent a disruptive "no-deal" Brexit.

But the backlash was swift and fierce.

Both ruling Conservative and opposition Labour lawmakers criticised May's Withdrawal Agreement Bill, or WAB, legislation which implements the terms of Britain's twice-delayed departure.

Some intensified their public efforts to oust May and there were reports that her own cabinet ministers could move against her.

"There is one last chance to get it right and leave in an orderly fashion. But it is now time for Prime Minister Theresa May to go - and without delay," Conservative lawmaker Tom Tugendhat, chairman of parliament's Foreign Affairs Select Committee, wrote in the Financial Times.

"She must announce her resignation after Thursday's European (Parliament) elections." The protracted impasse in London over the terms of Brexit means it is unclear how, when or even if Britain will leave the European club it joined in 1973. The current deadline to leave is Oct. 31.

May's latest offer has enraged eurosceptics opposed to a second referendum, and fails to go far enough for those who want to give the public another say in the hope of stopping Brexit altogether.

Despite the criticism, May stood firm during more than two hours of questions in parliament, urging lawmakers to back the bill and then have a chance to make changes to it, so they can have more control over the final shape of Brexit.

"In time another prime minister will be standing at this despatch box," May said, acknowledging that her leadership was drawing to a close.

"But while I am here, I have a duty to be clear with the House (of Commons) about the facts. If we are going to deliver Brexit in this parliament we are going to have to pass a Withdrawal Agreement Bill," she told MPs.

May has so far fended off attempts to oust her by promising to set out a departure timetable once parliament has had a chance to vote on the legislation.

Asked by eurosceptic lawmaker Jacob Rees-Mogg whether she really believed in the new deal she had proposed or whether she was simply going through the motions, May said: "I don't think I would have been standing here at the despatch box and be in receipt of some of the comments I have been in receipt of from colleagues on my own side and across the house if I didn't believe in what I was doing," she said.

Reuters