British Foreign Secretary Boris Johnson resigned on Monday a day after Brexit Minister David Davis said that he was leaving his post. Davis and his deputy dramatically quit overnight over Mays plan to retain strong economic ties with the European Union even after Britain leaves in March next year. Brexit cheerleader Johnson then delivered a stunning second blow when he also marched out, triggering speculation that May could face an imminent leadership contest. Mays Brexit plan -- agreed by the cabinet on Friday in the hope of unblocking negotiations with Brussels due to resume on Monday -- has now cost her two of her top four ministers, throwing her administration and authority into turmoil. "This afternoon, the prime minister accepted the resignation of Boris Johnson as foreign secretary," her Downing Street office said in a three-sentence statement. "His replacement will be announced shortly. The prime minister thanks Boris for his work." Johnson criticized the Brexit blueprint in private but has so far refrained from public comment. There was no immediate statement from Johnson. Some euroskeptic lawmakers dream of replacing May with a staunch Brexiteer such as Johnson, a populist, polarizing politician who has never made a secret of his ambition to be prime minister. Downing Street swiftly appointed euroskeptic housing minister Dominic Raab to Daviss job, and said May was looking forward to working with him to deliver Britains departure from the EU in March. Minutes after Johnson quit, May defended her Brexit plan to lawmakers in the House of Commons — with Johnson absent from his usual place on the Conservative front bench. She said she and the two departed ministers "do not agree about the best way of delivering our shared commitment to honoring the result of the referendum" in which voters opted to leave the EU. Mays plan seeks to keep the UK and the EU in a free-trade zone for goods, and commits Britain to maintaining the same rules as the bloc for goods and agricultural products. May said that was the "only way to avoid a hard border" between the UKs Northern Ireland and EU member Ireland. Uncertainty over whether tariffs and immigration checks would be introduced at the border has been a major stumbling block in negotiations between Britain and the European Union. The resignation of Davis, with a stinging warning that Britain was "giving too much away too easily" in Brexit talks, was a blow to May just days after she declared a truce among her warring ministers. All eyes are now on the next move by Brexit hardliners in her Center-right Conservative Party. But the appointment of Raab, a leading Brexit supporter, suggests Tory Brexiteers are divided. Davis himself said it would be "wrong" if his departure led to a full-fledged rebellion, insisting that "of course" May would survive. European Commission spokesman Margaritis Schinas said the change of ministers was not a problem and that the EU was ready to negotiate "24/7". The EU "will continue to negotiate in goodwill, bona fide, with Prime Minister May and the UK negotiators in order to reach a deal", he said. May spoke to Commission chief Jean-Claude Juncker, EU president Donald Tusk and the leaders of Ireland, Sweden and Malta over the weekend to discuss her plans, and is meeting Austrian Chancellor Sebastian Kurz in London later Monday.