Britain's Prime Minister Theresa May at center right front row, speaks to lawmakers in the House of Commons, London, Wednesday March 13, 2019. Photo: Jessica Taylor/UK Parliament via AP.

London - British members of parliament are to begin voting on alternatives to Theresa May's unpopular withdrawal agreement with the European Union on Wednesday, as the prime minister struggles to keep control of the Brexit process and her own party.

Lawmakers voted on Monday to take control of the parliamentary process amid disagreement over how the country should deliver on the result of the 2016 Brexit referendum, when 52% of voters opted to leave the bloc.

Debate on the so-called indicative votes is expected to start at around 2pm, with voting to take place later Wednesday.

The options are expected to include a second referendum and deals that would keep Britain in a much closer relationship with the EU than the one negotiated by May.

A definitive result is unlikely given the number of suggested alternatives. A second round of voting is to be held on Monday.

May is facing turmoil in her Conservative Party, following the resignation of three more junior ministers on Monday and calls for her to resign.

Unable to get her hard-won deal through the House of Commons, due largely to a controversial "backstop" mechanism that seeks to prevent a hard border on the island of Ireland, the prime minister has stalled on holding a third vote on the deal fearing another defeat.

She is expected to give a closed-door speech to the party's influential 1922 Committee on Wednesday to rally support.

May has said she would not commit her government to acting on the results of the indicative votes.