The first fines for lockdown breaches in Downing Street are expected to be issued imminently after Scotland Yard concluded that laws were broken at the heart of government, sources have told the Guardian. Multiple government insiders said the Metropolitan police had made referrals for the first tranche of fixed penalty notices (FPNs) connected with parties and gatherings being investigated by police in No 10 and the Cabinet Office. It is understood the Met are expected to issue around 20 fines related to the most straightforward cases, though more are expected to follow. It comes two months after the force began examining material from the Whitehall inquiry carried out by the senior civil servant Sue Gray into multiple alleged breaches of Covid rules. The Met has sent questionnaires to more than 100 members of staff and aides, including Boris Johnson and his wife, Carrie; the head of the civil service, Simon Case; and the prime minister’s former principal private secretary, Martin Reynolds. Last week, the force said it intended to start questioning witnesses, with no FPNs issued so far. The announcement suggested officers had not yet found breaches that meet the evidentiary threshold for fines to be issued without further interviews. In total, police are investigating 12 separate events in 2020 and 2021, six of which Johnson is said to have attended. Scotland Yard said it had obtained more than 300 photographs and 500 pages of documents showing what Gray’s inquiry believes to be potential rule-breaking. Images include photos taken at parties and those taken from security-system cameras showing when people entered and exited buildings. The investigation is being carried out by detectives from the force’s special enquiries team, which focuses on sensitive cases. It has been led by Jane Connors, the force’s deputy assistant commissioner and lead for Covid enforcement. Paperwork from the Met is sent to Acro, the criminal records office, for the issuing of fines. The scandal over alleged Covid law breaches has repeatedly threatened Johnson’s premiership and led to a number of MPs calling for a vote of no confidence. Gray, who has been able to publish only a redacted version of her investigation, is planning to release a full report once the Met has concluded its work. The controversial Downing Street gatherings included a summer drinks party where attenders were invited to “bring your own booze”, leaving dos for civil servants and an alleged gathering in Johnson’s flat. No 10 has promised to reveal if the prime minister receives a FPN but has so far declined to say whether he has been interviewed by police. His allies are understood to believe he will not be questioned because the Met said they wanted to speak to witnesses rather than those under investigation. Ministers have publicly expressed confidence that Johnson will not be issued with a penalty by police. Oliver Dowden, the Tory co-chair, told LBC: “The prime minister is actually absolutely resolutely clear that he is not going to be subject to a fixed-penalty notice because he is confident that he has not broken the law.” A slew of senior Conservatives had privately said they expect a vote of no confidence in Johnson to be triggered if a FPN was issued. At least two Conservative MPs, Douglas Ross and Andrew Bridgen, have withdrawn letters of no confidence in Johnson, citing the inappropriateness of a leadership contest at a time when Russia has invaded Ukraine.