Detectives investigating alleged breaches of Covid-19 regulations in Downing Street will begin contacting people this week asking for an "account and explanation".
The Met Police said police would contact more than 50 people in the coming days.
It said officers from what has been named Operation Hillman will be sending out "formal questionnaires".
The document, which has formal legal status, asks for an account and explanation of the recipient’s participation in an event.
Recipients will be informed that responses are required within seven days.
The Met said contact was being made in relation to eight dates between May 20, 2020 and and April 16 2021.
It said in a statement: "Detectives, working for the Met’s Special Enquiry Team, continue to examine more than 500 documents and 300 images provided to them by the Cabinet Office and will be requesting further information from the Cabinet Office to assist with the investigation.
"There may be also be a need to contact further people in the coming days and weeks - should they be identified as having taken part in an event and having potentially breached regulations.
"It should be noted that being contacted does not mean a fixed penalty notice will necessarily be issued to that person. Nevertheless, if following an investigation, officers believe it is appropriate because the Covid regulations have been breached without a reasonable excuse, a fixed penalty notice will normally be issued.
"We understand the interest in and impact of this case, and are progressing the investigation at pace. We are committed to completing our investigations proportionately, fairly and impartially."
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