British Prime Minister Theresa May has stepped down as leader of the governing Conservatives, officially triggering a contest to replace her that could see her party embrace a tougher stance on Brexit.

Ms May announced she would step down last month after failing to deliver Britain’s departure from the European Union on time, deepening a political crisis in a divided country struggling to move on from a 2016 referendum on Brexit.

She will continue to work as prime minister until her party elects a new leader, a crowded race that will be defined by Brexit and competing approaches on how to deliver Britain’s biggest foreign policy shift in more than 40 years.

“For the remainder of her time in office, she will be building on the domestic agenda that she has put at the heart of her premiership,” her spokeswoman told reporters on Friday.

The contest to replace Ms May is gathering pace with Brexit campaigner Boris Johnson a favourite.

Meanwhile another leading contender, Michael Gove, has admitted to using cocaine on several occasions and has “deep regrets” about taking the drug.

“It was a mistake. I look back and I think I wish I hadn’t done that,” he said.

“It was 20 years ago and yes, it was a mistake. But I don’t believe that past mistakes disqualify you.”

Ms May, once a reluctant supporter of EU membership who emerged from the chaos after the 2016 referendum as prime minister, steps down with her central pledge – to lead Britain out of the bloc and heal the country’s divisions – unfulfilled.

Her team has been keen to shape her legacy beyond the Brexit failure, but she bequeaths to her successor a nation where traditional political divides are being eroded by strong beliefs on whether Britain should leave the EU, and how it should do so.

The contest to replace her has been heating up for weeks, with candidates arguing over the rights and wrongs of a so-called no-deal Brexit, or leaving the EU without a deal.

Official nominations will be received on Monday. The selection process should be completed by the end of July.

Former foreign minister Boris Johnson is championing a tougher stance on Brexit, saying Britain should leave with or without a deal by the new deadline of Oct. 31.

He is seeking to persuade Conservatives that he is the only candidate who could win a new national election for the Conservative Party.

Other leading contenders include the current foreign minister, Jeremy Hunt, and environment minister Michael Gove, who take a less hardline stance on Brexit.

But Michel Barnier, the EU’s Brexit negotiator, said on Friday any new prime minister will still face the problem of what to do with the Irish border, in order to secure frictionless trade, after Britain leaves the bloc.

-AAP