A defiant British Prime Minister Theresa May has vowed to contest a leadership challenge “with everything I’ve got” after her Conservative Party colleagues triggered a spill motion on Wednesday.

Highlighting her desire of “taking back control of our borders, laws and money” by finalising a Brexit deal that people voted for, Mrs May told the waiting media pack outside the PM’s official residence at 10 Downing Street that any leadership change could result in the Brexit process being delayed or extended beyond the existing March 29 deadline.

A vote on Mrs May’s leadership will be held in the House of Commons between 5am and 7am, Australian time.

The ballot has been triggered by the threshold of 48 letters of no confidence in Mrs May’s leadership being reached, chairman of the 1922 backbench committee Sir Graham Brady said.

The blow comes after Mrs May has struggled to gain support for her deal from the European Union, after 18 months of negotiations.

Foreign Secretary Jeremy Hunt said he would be supporting Mrs May.

"I will contest that vote with everything I've got" – UK Prime Minister Theresa May says she will "stand ready to finish the job" as no-confidence vote is triggered

Follow live updates: https://t.co/gTH05gW8Yy pic.twitter.com/TeFWGMjVCj

— BBC Breaking News (@BBCBreaking) December 12, 2018

Ms May’s stunning move on Tuesday morning (Australian time) to cancel a parliamentary vote on her Brexit deal – admitting it had no hope of passing – compounded the frustration.

It opens up an array of options for the United Kingdom, including a disorderly Brexit with no deal, another referendum on EU membership, or a last-minute renegotiation of the PM’s deal.

Announcing the delay, Mrs May admitted her Brexit deal “would be rejected by a significant margin” if MPs voted on it.

“We will therefore defer the vote scheduled for tomorrow and not proceed to divide the House at this time,” she said, adding that the UK would go back to the EU and ask for changes to the deal.

The EU executive earlier said it would not renegotiate its Brexit agreement.

“We have an agreement on the table,” a spokeswoman for the EU Commission told reporters on Monday night, adding: “We will not renegotiate.”

The response to Mrs May’s action was widely condemned.

Opposition Leader Jeremy Corbyn said the UK no longer had “a functioning government”. 

A small Northern Irish party that props up Mrs May’s Conservative minority government called the situation a shambles, and Scottish nationalists pledged to support a vote to bring down the government.

The decision to halt the vote came just hours after the EU’s top court ruled that Britain could unilaterally withdraw its decision to leave the bloc on March 29.

In an emergency judgement delivered on Monday night, the European Court of Justice (ECJ) said: “The United Kingdom is free to revoke unilaterally the notification of its intention to withdraw from the EU.”

The ruling is in line with an opinion delivered last week by a court legal adviser. That had boosted the hopes of British Brexit opponents that a new referendum could be held that would prevent Britain’s scheduled departure.