British Prime Minister Theresa May has on Wednesday night defeated a challenge to her leadership of the Tory Party, winning a confidence vote by 200 MPs to 117.

It was confirmed that the necessary total of 47 letters of no confidence, amounting to 15% of the total number of Tory MPs, was finally reached on Wednesday morning. The news triggered a day of drama at Westminster.

Mrs May made a public statement before the crucial vote began. She said that changing Conservative leader would "put our country's future at risk and create uncertainty when we can least afford it" and could lead to Brexit being delayed or prevented.

Tory Cabinet minister Amber Rudd told reporters May had also made a vow to quit as party leader ahead of the next scheduled general election in 2022, in a last-minute bid to win over waverers.

Despite her victory, and with opposition to her now including the DUP who have withdrawn their support from her minority government, it remains unclear how May can win the support of Westminster for any Brexit deal.

After winning the confidence vote, May called for backing from "other parties" for the deal she reached with the EU last month. She also vowed to secure a legal statement of assurances from the EU in regard to limiting the 'backstop'. That provision is intended to ensure no remilitarisation of the border through Ireland, but is bitterly opposed by the DUP and the Tory right-wing.

May's support of 200 MPs was actually one more than the number of votes she received in the 2016 leadership election, and significantly, her victory means she cannot face a similar internal challenge for another year.

But May's weakness "has completely immobilised the government at this critical time for the country", the chairman of the main opposition Labour Party said.

"The prime minister's half-baked Brexit deal does not have the backing of her cabinet, her party, parliament or the country," Ian Lavery said in a statement. "The Conservative Party's internal divisions are putting people's jobs and living standards at risk."

With less than four months left until Britain is due to leave the EU on March 29, British politics is embroiled in turmoil, opening up the possibility of a crash, no-deal Brexit. Pressure is growing for a new referendum on Brexit, and there have also been calls for referenda in the North of Ireland and Scotland on leaving the union with England and staying within the EU.

Sinn Fein leader Mary Lou McDonald said she had told Mrs May in a phone call that a referendum on Irish unity must be called as a matter of urgency if there is no final deal agreed by Westminster.

"Irish Unity is the ultimate contingency to protect our interests in the event of a crash Brexit," she said.