Three sources told the Guardian that the breach was deemed so serious that Mordaunt was prepared to seek a D notice to warn any outlet considering publishing the information that it risked compromising Britain’s national security. But Williamson, who denied leaking national security information that saw him ousted from cabinet in 2019, said he had nothing to do with the second serious alleged leak. A former government spokesman said it was believed by senior MoD officials at the time that the leak “could only have come from Gavin” and that “our people’s lives were put at risk by it”. They declined to discuss the details of the alleged leak, for the same security reasons, but said the matter was a major concern during Mordaunt’s brief spell as defense secretary between May and July 2019. Another source said officials believed “100%” the leak “came directly from Williamson” and that Mark Sedwill, the then cabinet secretary and national security adviser, was briefed by the security services. The third source said Mordaunt successfully secured the leak and that the move had never previously been made public. A spokesman for Williamson told the Guardian that the allegation that he was the culprit behind a second major leak was “categorically untrue” and added: “He has no knowledge of any such thing or any involvement with it.” The secretary of the Defense and Security Media Advisory Committee can issue notices to ask the media not to report certain information on grounds that could harm UK national security. If deemed necessary, the commission’s secretary, currently an ex-army officer, will issue a letter outlining specific concerns after consultation with the relevant government department. However, it is not mandatory to follow the tips. A government spokesman said: “We do not comment on matters of national security or alleged investigations into leaks.” It was also disputed that Williamson had been formally suspected or accused within Whitehall of being responsible for a second major leak. Mordaunt, who is now leader of the Commons, declined to comment. Williamson was sacked by former prime minister Theresa May in May 2019 for leaking to the Daily Telegraph details of a controversial national security council discussion on how to handle Chinese phone maker Huawei. He denied being the source of this leak. Williamson resigned in dramatic fashion on Tuesday night following a series of allegations of bullying and threatening behavior when he was a cabinet minister. A former Foreign Office official made a formal complaint on Tuesday after the Guardian revealed that Williamson told them to “cut your throat”, in what they felt was an ongoing campaign of intimidation. It is unclear whether the prime minister, Rishi Sunak, was aware of the earlier security concern when he appointed Williamson as minister of state in the Cabinet Office. His short-lived responsibilities included the UK’s Global Stability and Conflict Security Fund and the Government Communications Service, which houses departmental press officers. A number of ministers, advisers and officials believed Williamson was a leaker and tried to pass on sensitive classified material to the press – although Williamson himself denied passing on information about Huawei. A former Downing Street official told the Guardian that there was “substantial information” that proved Williamson was the leaker and not all of it was put into the public domain at the time. “We didn’t want to reveal our methods,” the former employee said. There was surprise in Downing Street that Williamson so vehemently denied being the source – at the time, he was reported to have sworn on the lives of his children that this was not the case – when No 10 believed he had all the evidence he needed to prove the participation of . “The only explanation for his denials at the time was that he wanted to make a comeback,” the former employee said. Williamson was reappointed education secretary by Boris Johnson but was sacked in a reshuffle before being reinstated by Sunak.
