May was under pressure from Eurosceptic MPs to ensure that Patel is replaced by a pro-Brexit MP like her predecessor to maintain a balance within the UK Cabinet.
Mordaunt, 44, is a pro-Brexit Conservative party MP for Portsmouth North who has held a number of junior ministerial posts, including the post of disability minister in the department for work and pensions from where she has now been promoted.
The quick Cabinet reshuffle had become necessary after 45-year-old Patel was forced to resign from her Cabinet post in charge of the Department for International Development (DfID) yesterday after days of controversy surrounding a series of unauthorised meetings she had held with Israeli officials, including Prime Minister Benjamin Netanyahu.
"While my actions were meant with the best of intentions, my actions also fell below the standards of transparency and openness that I have promoted and advocated. I offer a fulsome apology to you and to the Government for what has happened and offer my resignation," Patel had said in her resignation letter addressed to May.
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"From the backbenches I will continue to take an active role...speak up for our country, our national interests and the great future that Britain has as a free, independent and sovereign nation," she noted.
In her reply, May said: "As you know the UK and Israel are close allies, and it is right that we should work closely together. But that must be done formally, and through official channels".
"That is why, when we met on Monday I was glad to accept your apology and welcomed your clarification about your trip to Israel over the summer. Now that further details have come to light it is right you have decided to resign," May said.
However, she was summoned back to Downing Street by May after it emerged that there were further meetings that had potentially breached ministerial protocol.
It is understood that Patel met Israel's public security minister, Gilad Erdan, in the UK Parliament complex in early September and an Israeli foreign ministry official, Yuval Rotem, in New York later that month.
May was reportedly told about the unreported New York meeting during Patel's initial apology conversation at Downing Street on Monday but only learned about the unreported meeting with Erdan after the talks.
Patel's resignation marks the second high-profile Cabinet shake-up for May within a week, after Michael Fallon stepped down as defence secretary amid allegations of sexual misconduct.
With a Budget statement just days away and deadlocked Brexit talks resuming this week ahead of a make-or-break EU summit next month, Patel's exit has only added to May's leadership woes with many predicting her own exit from Downing Street by the end of this year.
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