He is expected to launch a clear-out of key Number 10 figures ensnared by the row, overhauling his top team of advisers and officials, in response to the probe.

Officers ‘only too willing’ to co-operate

Officers deployed to guard Downing Street would have a detailed knowledge of the comings and goings at Number 10 and would therefore be in a position to corroborate some of the most damning allegations that have emerged in recent weeks, such as whether a suitcase of alcohol was brought in to one event on the eve of the Duke of Edinburgh’s funeral.

They may also have been in a position to comment on the wider drinking culture in Downing Street during lockdown, and whether they issued any warnings to party attendees or officials.

Amid reports that some Number 10 staffers have been “circling the wagons” by holding back information from the Gray inquiry, and even deleting incriminating photographs and WhatsApp messages, the police officers are likely to be seen as impartial observers.

While police officers cannot be compelled to speak to Ms Gray – unlike Downing St staff – it is understood they were “only too willing” to co-operate.

One source said on Sunday night: “Met officers have spoken to Sue Gray now, as you would expect, and have been able to provide a lot of information.”

Asked how significant the material they had disclosed was, the source added: “Put it this way, if Boris Johnson is still Prime Minister by the end of the week, I’d be very surprised.”

Scotland Yard under the spotlight

Scotland Yard has come under fire for refusing to launch a criminal investigation into allegations of parties during lockdown.

However, sources have said that the officers on duty in Downing Street have “nothing to hide” and their testimony is beyond reproach.

A Scotland Yard spokesman would not be drawn on whether officers had been interviewed by Ms Gray, but added: “The Met has ongoing contact with the Cabinet Office in relation to this inquiry.”

On Tuesday, Dame Cressida Dick, the Met Police commissioner, is expected to be questioned about “partygate” when she makes her regular appearance at the London Assembly police and crime committee.