British Prime Minister Theresa May has ended her turbulent reign as Tory leader as rivals to replace her step up their campaigns.

The low-key resignation saw Mrs May write to the joint acting chairmen of the backbench Conservative 1922 Committee, Charles Walker and Cheryl Gillan, confirming the announcement she made a fortnight ago in Downing Street.

She will remain Prime Minister until Tory MPs and members complete the process of choosing her successor in late July.

"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," a spokeswoman told reporters

Mrs May announced her resignation two weeks ago, following strong resistance in the party to her attempts to get the House of Commons to vote for a fourth time on the EU Withdrawal Agreement.  

The contest to elect her successor will officially begin next week and Mrs May will remain as acting party leader and prime minister until then.

Under the timetable set out by the party high command, it is expected the new leader will be in place in the week beginning 22 July following a postal ballot of the party's 120,000 grassroots members.

Mrs May prepares to step down amid a growing row with Chancellor Philip Hammond over her plans to leave with a series of big spending announcements - including a multi-billion pound overhaul of England's schools and colleges - according to the Financial Times.

The reported row comes after Downing Street defended the need for ambitious action to tackle climate change following warnings from the Treasury that cutting the UK's greenhouse gas emissions to zero by 2050 will cost £1 trillion.

Even as the formalities around Mrs May's departure were taking place, the 11 contenders so far to declare in the race to succeed her were engaged in increasingly bitter exchanges.

Foreign Secretary Jeremy Hunt warned there would be "no future" for the party unless Brexit is resolved.

Boris Johnson, the bookmakers' favourite to replace Mrs May, has said that unless the UK's withdrawal from the European Union is completed by 31 October, an election would see Labour leader Jeremy Corbyn in Downing Street.

Former Brexit secretary Dominic Raab was at the centre of a political storm after he suggested he could be prepared to suspend Parliament to prevent it blocking a no-deal Brexit on 31 October.

Home Secretary Sajid Javid became the latest contender to denounce the idea - branding it "anti-democratic and anti-British".

Speaking to the British Future think tank yesterday, Mr Javid said that while he wanted to leave the EU by the cut-off date of 31 October, he accepted Parliament was entitled to a say.

"I wouldn't prorogue Parliament. That is a complete nonsense. My policy would be to do everything I can to leave the European Union on October 31," he said.

"If it got to a point where I had to choose between no deal or no Brexit, I would pick no deal. But whatever I do, Parliament is going to want have its say on it and Parliament should have its say.

"Our Parliament is sovereign. I am not into this proroguing Parliament rubbish. It is just a complete nonsense and anti-democratic and anti-British."

Mr Javid also took a sideswipe at leadership front-runner Boris Johnson over his comments last year saying Muslim women who wear the burka looked like letter boxes.

"I think they they are wrong. I don't think they are the right comments. I don't think any serious politician should use language like that," he said.

Meanwhile, Michael Gove received a boost as Tory Party vice-chairman Kemi Badenoch announced she was quitting her post at Conservative headquarters to join his campaign.

She said she was supporting the Environment Secretary because she believed he could deliver on the 2016 referendum result.