The High Court will hear the first stage of a challenge against the Metropolitan Police over the force’s investigation into former prime minister Boris Johnson’s attendance at Number 10 parties during lockdown.

Mr Johnson received a fixed penalty notice (FPN) over a birthday party in the Cabinet Room in June 2020, but faced no further action over other gatherings covered by the Met’s Operation Hillman inquiry into events in No 10 and Whitehall.

However, according to a report by senior civil servant Sue Gray, released in July last year, Mr Johnson gave a leaving toast for departing communications chief Lee Cain on November 13 2020, days after ordering England’s second national lockdown.

Images published in her report showed Mr Johnson apparently raising a glass while surrounded by colleagues and bottles of wine.

He also gave a speech at an alcohol-fuelled leaving do for two No 10 officials on December 17 2020, with around 20 people in attendance, Ms Gray said.

Legal campaign group the Good Law Project (GLP) has launched a legal challenge, alongside former deputy assistant commissioner of the Met Lord Paddick, against the force over its investigation.

The GLP says the Met failed to send questionnaires to Mr Johnson, and has since failed to explain why, or how the force concluded his attendance at other events was lawful.

The group will ask Mr Justice Swift to grant permission for a judicial review of the Met’s handling of the investigation at a hearing in London at 10.30am on Wednesday.

The force issued 126 FPNs to 83 people at events in Downing Street and Whitehall, including to other attendees at both the November 13 2020 and December 17 2020 gatherings.

Jo Maugham, GLP director, said: We can’t understand – and the Met won’t disclose – how Boris Johnson dodged fines for going to parties that junior civil servants were fined for attending.

“But what it looks like is special treatment for the powerful.”

Lord Paddick said: “My sole motivation is to ensure everyone is treated fairly and equally under the law as a result of the police carrying out their duty without fear or favour.

“Many fined for breaching lockdown rules will find this difficult to believe without further explanation from the Metropolitan Police.”