The senior civil servant investigating allegations of at least nine lockdown-breaking parties at Downing Street has been given access to a detailed log of staff movements in and out of the building from security data including swipecards. Whitehall figures say the inquiry by Sue Gray – who is expected to publish a report of about 25 pages this week – has been “forensic”, looking in “granular detail” at who was in the building for social gatherings, some of which went on into the early hours, and the precise timings of their arrivals and departures. Johnson and his staff, as well as civil servants and others who attended the events under investigation, are anxiously awaiting Gray’s conclusions this weekend. She has been assisted by six civil servants with HR experience. Many Tory MPs say they are holding off from deciding whether to call for the prime minister to resign until they see its conclusions, and hear the reactions of their constituents. Rumours have also been circulating in government in recent days that Gray may have details of yet another gathering in Downing Street, possibly in the PM’s flat and involving close friends of his wife, that has not yet come to light. Discovery of a 10th get-together when Covid restrictions were in place would seriously undermine Johnson’s attempts to survive the crisis. But senior Whitehall sources also say the information from data logs that record movements for security reasons could be decisive, as they will have given Gray conclusive proof of who was where and when, and how many people remained after normal working hours – details that she would otherwise have lacked. “This information is conclusive,” said a source who knows Gray. “This is not someone saying ‘I saw him or her at a party’. This is the proof of who was where, how many people were inside the building at any one time. “She will have been looking at all that information, which is far more valuable than people’s say so. It is the evidence.” The source added that the security logs would also have allowed Gray to draw conclusions about the culture at No 10, which appears to have allowed parties to have become regular events. “If you get the data and you find a large group all swiped out at 1am in the morning, then it looks very much like it was a party and if that was going on regularly you can judge from that.” Friends of Gray who have worked with her say she will be scrupulously fair but also “ruthless” in pursuit of the truth. One former colleague and friend said she was in no mood to allow civil servants alone to take the flak. “She has shown before in previous inquiries that she will hold civil servants to account because she is very strong on civil service behaviour, but if she thinks politicians or others should take responsibility she will make that very clear,” the source said. While it is possible that Gray will name some very senior civil servants and high-up figures in government in her main 25-page report, she is expected to follow precedent and not make public the identities of junior civil servants or special advisers. Their names are expected to be listed in another document that will remain confidential and be sent to human resources teams in their respective departments, who would then be responsible for determining what sanctions, if any, should be imposed. After another torrid week for Johnson, which saw the defection of the Tory MP Christian Wakeford to Labour, the prime minister has been spending the weekend calling backbenchers to try to shore up his position. Fewer than a dozen Tory MPs are believed to have written to the chair of the 1922 Committee to demand a vote of confidence, but many more say they will do so if the Gray report concludes that the PM broke lockdown rules, and more incriminating information emerges. If 54 or more write in, a vote of confidence must be held. If Johnson loses that, he has to resign. A meeting of the 1922 Committee on Wednesday will be a key judge of the Tory mood. Wakeford told the Observer that Johnson was doomed. “If Boris Johnson is hoping Sue Gray’s report will save his skin then he’s in for a shock. The rot has already set in and many of my former colleagues have already reached the conclusion that he’s unfit to lead the Conservative party. Not just because he’s an electoral liability but because he’s actually unfit to run the country. “Are there enough of them to trigger a leadership election? I’m sure there are. Will they go through with it? That’s a matter for them. What I do know is that in seats like Bury South the voters have made up their minds about him. So it’s just a question of whether MPs choose to listen to their constituents or the party whips.” Ruth Davidson, the former Scottish Tory leader, said the PM was not fit for office. “I think one of the reasons he is in such a perilous situation is not just because of the apparent rule-breaking, although that is a big part of it, but because there is a fatigue even within the party and certainly by my MP colleagues for the drama that has been emanating from No 10,” she said.