Police will not open a criminal investigation into the leak of secret information from the National Security Council unless the case is referred to them by the Government, the country's most senior officer has indicated.
The investigation was launched after the Daily Telegraph newspaper reported that May had chose to allow Chinese technology company Huawei to build non-core parts of the 5G network, despite national security concerns.
Professor Tony Travers, a specialist in British government at the London School of Economics and Political Science's department of government, said: "While this issue adds further to the government's difficulties, it makes Mrs May look more powerful".
He once boasted that having "made" Mrs May "I can also break her".
However an inquiry by the National Security Adviser, Sir Mark Sedwell has stopped short of recommending Mr Williamson is also prosecuted for an offence. May as Prime Minister.
In an episode of "Yes Minister", the iconic political comedy, Sir Humphrey Appleby, the infamous civil servant, assures his often-anxious colleague Bernard Woolley, concerned about a potential leak inquiry being threatened by Downing Street, that there was nothing to worry about as they were only ever set up and rarely resulted in anything substantive.
The announcement has led to calls for a criminal investigation into the matter.More news: In a stunner, Country House wins Kentucky Derby via disqualification
Theresa May sets out her justification for sacking Gavin Williamson.
Mr Williamson, a former Tory whip, helped run Theresa May's successful leadership campaign, was rewarded for that role with this surprise promotion to replace Michael Fallon in November 2017.
In a letter to Williamson, May said that the probe "provides compelling evidence suggesting your responsibility for the unauthorized disclosure".
In firing Williamson on Wednesday, May said an investigation had left no other credible explanation for the leak except that Williamson was responsible.
"The prime minister thanks all members of the National Security Council for their full cooperation and candour during the investigation and considers the matter closed".
May, the report said, had overruled concerns expressed at the NSC meeting by her Home Secretary Sajid Javid, Foreign Secretary Jeremy Hunt, Defence Secretary Gavin Williamson, International Trade Secretary Liam Fox, and International Development Secretary Penny Mordaunt.
I'm sorry that you feel current leaks from the Nationwide Safety Council originated in my Division.
"If the Cabinet Office were to send us a referral at any point that relates to apparent official secrets or leaks, we would assess that", she said.
The former head of the Central Intelligence Agency will meet Mrs May and Jeremy Hunt, the Foreign Secretary, in London next Wednesday.