An eleven minute phone call is what appears to have sparked Gavin Williamson’s spectacular and dramatic downfall from government.

When the defence secretary talked to Telegraph journalist Steven Swinford last Tuesday, he set in train a sequence of events that ended with the first leak-related sacking of a Cabinet minister in 70 years.

Communications records, showing that the pair spoke after two crucial meetings of the National Security Council (NSC) and Cabinet that day, are understood to have revealed the exact length and time of the call.

In a two-hour session with the official leak inquiry investigators last Friday, Williamson strenuously denied that he had discussed any confidential material from the NSC meeting, never mind the Huawei case. He’d chatted instead about the Tory leadership, Brexit and other matters, he said.

But it’s clear that his explanation simply didn’t wash with the inquiry – or with Theresa May.

Just as importantly, the prime minister felt that one of her most valued and trusted ministers had not cooperated as fully as he should have with the investigation.

In his letter of reply, Williamson made clear he wasn’t going without a fight. And in his sights was the PM’s all-powerful Cabinet Secretary and national security adviser, Sir Mark Sedwill.

His suggestion that “a thorough and formal inquiry” would have proved his innocence was a clear jibe at Sedwill, who has raised eyebrows among several ministers by retaining his dual role since he succeeded Sir Jeremy Heywood last year.

Williamson’s defence is that far from being obstructive he has been open from the start. Yet for some in Whitehall and Westminster, there has been an almost comical element to his explanations since the Daily Telegraph printed its bombshell report on Huawei last Tuesday night.

He has told investigators – and colleagues – that he hadn’t even known about the Telegraph story until he heard it on BBC Radio 4’s Today programme the following morning.

And when he did, he was allegedly outraged at the way the BBC portrayed the NSC decision as a positive story that depicted the PM as curbing Huawei’s activities, rather than focusing on the risks of allowing the Chinese firm access to the UK’s 5G network for the first time.

Crucially, Williamson that morning personally confronted de facto deputy PM David Lidington, and told him how furious he was at the leak, even declaring to his colleague that the culprits behind the leak could be specialist officials who support the NSC.

Lidington, who has overall responsibility for the Cabinet Office secretariat, was not amused by the attempt to blame civil servants in his department. And members of the secretariat were equally appalled at the questioning of their integrity.

Once Williamson had calmed down however, and saw the Telegraph account, it’s claimed he realised he had made an error in blaming the Cabinet Office.

Most importantly of all, he actually openly admitted last Wednesday to colleagues that he had spoken to Swinford himself. At that point, No.10, already furious at the way the classified report on Huawei had emerged, became swiftly involved.

As the hunt for the leaker began in earnest, one by one those ministers who attended the meeting denied they had been responsible for the security breach.

Williamson put out a categoric denial. But so too did all the other ministers who had allegedly expressed concerns about the Huawei decision: foreign secretary Jeremy Hunt, home secretary Sajid Javid, international trade secretary Liam Fox and international development secretary Penny Mordaunt.

The investigators were determined this would be different from usual leak inquiries that rarely end up with any conclusion. This was different because the NSC hears from not just ministers but all the heads of MI5, MI6, GCHQ, chief of defence staff and the chairman of the Joint Intelligence Committee.

Set up in 2010 partly to learn lessons from Tony Blair’s sofa government role in the Iraq War, the new body’s deliberations were seen as sacrosanct. “It’s very important that they can provide information in a very candid way in total confidence that that information will not be disclosed,” the PM’s spokesman said on Wednesday night.

“If they do not have that confidence, you risk undermining the decision making process which in turn harms national security. It’s absolutely the core job of the prime minister to protect national security and the national security decision making process. That’s the context.”

Sedwill, having ordered the full-scale investigation, could not lead it himself. He, along with the prime minister herself, was one of those in the Cabinet room when the NSC discussed the Huawei case.

As a result, both he and May were interviewed for the inquiry, as well as everyone else who took part in the discussion.

The ‘Hua-dunnit’, as some government insiders jokingly called the probe, suddenly became very serious indeed. Mobile phones were handed in, comms records gone through and witness statements taken. WhatsApp messages and texts to journalists were trawled through and questions asked.

Throughout it all, Williamson maintained his innocence and that of his staff.

Yet it was on Wednesday afternoon that the investigators finally presented their findings to May. She was in the middle of exhaustive preparations for a grilling by the liaison committee of senior MPs, due at 3pm, when the news came through: her defence secretary was the one who was most likely to have been responsible.

May had to go straight to Portcullis House for her 90-minute session with the committee. But during the hearing, she appeared more relaxed and confident than usual.

When a question on Huawei came up right at the end, she made a strong defence of her position without letting slip the devastating information she had seen minutes earlier.

Just before 5pm, Williamson was called into May’s Commons office and the pair of them spent 30 minutes discussing the ‘compelling evidence’ of his role in the leak.

He again protested his innocence and refused to resign, but the PM made her mind up that she simply could not trust him. Within half an hour, the shock news was put out by No.10 that he had been fired.

May swiftly decided that his dismissal should draw a line under one of the most embarrassing and damaging episodes of her premiership. Yet her refusal to treat the matter as meriting a criminal investigation will rapidly become the next political headache.

It may be that some of the evidence against Williamson, by the very nature of the confidential way it was obtained, is inadmissable in a court of law. It’s further argued by some that the burden of proof is much lower in a political judgement about a sacking than in a criminal case involving state secrets.

Even if there is not a case for prosecution under the Official Secrets Act, there is a lesser charge of misconduct in public office that is sure to be seized on by critics. For his part, Williamson looks like he will go on the offensive, challenging No.10 to release the ‘compelling evidence’ against him.

Many Tory MPs with military backgrounds, who believe Williamson was right to express concern over the Huawei case, are as equally convinced he was always the wrong man for the job.

The defence secretary already had a poor reputation among several in the military and his standing among fellow Tory MPs was often the topic of ridicule.

Known in the Commons Tea Room as ‘Private Pike’, after the hapless rookie in TV’s Dad’s Army, part of the antagonism stemmed from his previous job as one of the youngest ever Chief Whips in history.

From his Instagram boasts about his pet tarantula to his infamous line at the height of the Salisbury poisoning affair, when he said Russia should “go away and shut up”, his most scathing critics have often been fellow ministers.

When he was first appointed to the MoD top job, one minister of state said: “She’s gone mad. He’s a real slimeball, with his own leadership team in place.” As it happens, he’s been vehemently denying in recent months that he actually wants the PM’s job, and has talked instead of a ‘dream ticket’ as a running mate for another colleague.

Yet behind the scenes, May highly rated Williamson ever since he was plucked from obscurity by David Cameron and made his parliamentary private secretary. When she ran for leader after Cameron’s Brexit-inspired demise, the young fixer proved himself in corralling support for her team and was rewarded with the Chief Whip job.

During his time in the whip’s office Williamson further impressed May when he wooed the DUP in the wake of her disastrous election blunder, putting together a majority at a time when she was at her most rocky in office.

But some ministers still believe she laid bare her own poor judgement when she panicked and appointed him to defence secretary following Michael Fallon’s own resignation in November 2017. Williamson hadn’t had a single minute’s experience at the Commons despatch box beforehand.

As with her previous chief of staff Nick Timothy, some allies were baffled by the way she came to depend on the young Yorkshireman. Always keen to keep those close to her very close indeed, critics say that fatal weakness to indulge favourites has led frequently returned to bite her.

The problem for Williamson, in the eyes of some in Whitehall, is that the person May recently came to rely and depend on most was Sir Mark Sedwill. Making him her Cabinet Secretary, while keeping him as national security advisor, is what may have proved a key factor in the dramatic events of the past week.

As an ex-Chief Whip, Williamson knows where several political bodies are buried in the Tory party. The final irony is that his is now amongst them. Or as one fellow MP put it when they heard the news of his sacking over the leak: “There’s no coming back from this.”