Fighting back tears, Theresa May said on Friday she would quit after failing to deliver Brexit, setting up a contest that will install a new British Prime Minister who could pursue a cleaner break with the European Union.
May's departure deepens the Brexit crisis as a new leader, who should be in place by the end of July, is likely to want a more decisive split, raising the chances of a confrontation with the EU and potentially a snap parliamentary election.
"I've messaged Theresa May to personally thank her for her support on a number of issues of importance to New Zealand," New Zealand Prime Minister Jacinda Ardern said.
"New Zealand has been and will remain a close friend and partner of the UK and there's no question that will continue."
Politicians in her party and abroad paid tribute to her determination. French President Emmanuel Macron praised May's "courageous work" and US President Donald Trump said he felt bad for her.
"I like her very much, she is a good woman, she worked very hard," Trump said.
Former Foreign Minister Boris Johnson, the favourite to replace May, was first out of the blocks, saying Britain should be prepared to leave the EU without a deal to force the bloc to offer a "good deal".
Current Foreign Minister Jeremy Hunt also confirmed he would run for the leadership just hours after May, her voice cracking with emotion, said she would resign as Conservative Party leader on Friday, June 7, setting up a contest to succeed her.
"I will shortly leave the job that has been the honour of my life to hold," May said outside her Downing St official residence with her husband, Philip, looking on. "The second female Prime Minister, but certainly not the last.
"I do so with no ill will but with enormous and enduring gratitude to have had the opportunity to serve the country I love," said the usually reserved May.
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May, once a reluctant supporter of EU membership who won the top job in the turmoil that followed the 2016 Brexit referendum, steps down with her central pledge - to lead the United Kingdom out of the bloc and heal its divisions - unfulfilled.
"It is, and will always remain, a matter of deep regret to me that I have not been able to deliver Brexit," May said, adding that her successor would have to find a consensus to honour the 2016 referendum result.
Jeremy Corbyn, leader of the main opposition Labour Party, said the new Prime Minister must hold an election to "let the people decide our country's future".
Betting markets give Johnson a 40 percent implied probability of winning the top job.
He made his pitch at an economic conference in Switzerland, appealing to Brexit-supporting Conservative Party members by saying: "We will leave the EU on October 31, deal or no deal."
He said Britain could forge a "fantastic free trade relationship" with Europe after it quits the bloc but could also be a champion for global free trade.
Others tipped are Dominic Raab, a Brexit supporter and former Brexit secretary, with a 14 percent implied probability on his chances. Environment Secretary Michael Gove, former House of Commons leader Andrea Leadsom and Hunt each have a 7 percent probability, according to betting markets.
Defence Secretary Penny Mordaunt and International Development Secretary Rory Stewart each have a 4 percent chance of the top job while Home Secretary Sajid Javid has a 3 percent chance.