Downing Street police officers have reportedly been quizzed by Sue Gray as part of her 'partygate' probe.
Members of the Metropolitan Police's Parliamentary and Diplomatic Protection Command are said to have been interviewed as part of the investigation.
The unit would have been on duty when a series of gatherings are alleged to have taken place, potentially breaching lockdown rules.
According to reports, their statements have been described as 'extremely damning' and could form a key part of the probe.
Top civil servant Sue Gray is expected to deliver her report next week after gathering evidence on a string of potentially rule-breaking gatherings.
The Daily Telegraph reports that the senior official has also spoken to Boris Johnson, civil servants and political advisers, as well as accessed security pass logs and the Prime Minister’s official diary.
While police officers cannot be compelled to speak to investigators, unlike Downing Street staff, the outlet claims they were “only too willing” to co-operate.
A source said: “Met officers have spoken to Sue Gray now, as you would expect, and have been able to provide a lot of information.”
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Asked how significant the material they had disclosed was, they added: “Put it this way, if Boris Johnson is still Prime Minister by the end of the week, I’d be very surprised.”
A Scotland Yard spokesman added: “The Met has ongoing contact with the Cabinet Office in relation to this inquiry.”
It was also claimed that Ms Gray as part of her investigation has had access to the system that records when staff use their swipe cards to enter and exit Downing Street.
A log of all visitors and the names of those who sponsor their visit are also kept on the same system.
The inquiry comes after explosive claims emerged that Mr Johnson attended a leaving do before Christmas 2020 during which he gave a speech to mark the departure of his defence adviser Captain Steve Higham.
That claim, revealed by the Mirror, is the latest in a long line of allegations about rule breaking in Downing Street, with Ms Gray looking into a litany of possible events.
These include a "bring your own booze" garden party during the first coronavirus lockdown that Mr Johnson has admitted he attended - although he insists he understood it to be a "work event".
Previously, Education Secretary Nadhim Zahawi insisted Mr Johnson was safe in his job after being repeatedly asked about his future.
Mr Zahawi said the Prime Minister had done the right thing by apologising - and added: "He's human and we make mistakes".
