The government plans to keep secret the names of any ministers, MPs or senior political advisers who are fined for partying during lockdown, it has admitted.

The code of silence has enraged Westminster opposition parties, who say there must be transparency about whether the people who set Covid laws then subsequently broke them.

A Cabinet Office spokesperson told openDemocracy: “Following the long-standing practice of successive administrations, any specific HR action against individuals will remain confidential.”

Number 10 had previously promised to reveal if the prime minister receives a fixed penalty notice, the fine for which would be expected to be £100, but openDemocracy understands this pledge still stands.

Chancellor Rishi Sunak is among those thought to be at risk of a fine after he attended a gathering for Boris Johnson’s birthday in 2020. Police subsequently issued him with a questionnaire about the event. 

The Metropolitan Police announced today that it was ready to refer the first 20 breaches to the ACRO Criminal Records Office, which issues fines. The force said it would follow guidance from the College of Policing stating that anyone given an out-of-court penalty such as a fine should not be identified.

Angela Rayner, Labour’s deputy leader, said both Johnson and his chancellor Rishi Sunak should resign if they are fined. 

“The culture is set from the very top. The buck stops with the prime minister, who spent months lying to the British public, which is why he has got to go,” said Rayner.

Kirsten Oswald, the Scottish National Party’s deputy leader at Westminster, called for Number 10 to name everyone fined.

“The public will rightly want answers and accountability, and it is vital that there is transparency in this ongoing investigation and that must involve full disclosure of precisely who, among ministers and senior civil servants, is being fined for breaking the law,” she said.

The Covid-19 Bereaved Families for Justice group called for the prime minister to resign over the fines in a statement in response to the announcement.

“Frankly, bereaved families have seen enough. The PM should have resigned months ago over this. By dragging it out longer all he is doing is pouring more salt on the wounds of those who have already suffered so much,” they wrote.

Police are investigating 12 separate events in 2020 and 2021, which include a summer drinks party where attendees were encouraged to “bring your own booze”, several leaving dos for civil servants and an alleged gathering in Johnson’s own Number 11 flat. 

Johnson is said to have personally attended six of the events being scrutinised by the police. 

The Met has been investigating the alleged breaches for two months, during which it has sent questionnaires to more than 100 members of staff and aides, including Johnson and his wife Carrie. 

The force previously said it had been handed more than 300 photographs and 500 pages of documents as evidence from a Whitehall inquiry led by the senior civil servant Sue Gray.

In a statement on Tuesday, the Met said that there is a “significant amount of investigative material that remains to be assessed” and that further fines may be issued if the evidence threshold was met.