10 Downing St

Commissioner Cressida Dick said they were looking into "potential breaches of Covid-19 regulations" in Downing Street and Whitehall since 2020.

Boris Johnson told the Commons he welcomed the investigation as it would "give the public the clarity it needs" over the allegations.

His spokesman also said the PM did not believe he had broken the law.

Dame Cressida said the investigation was launched after the Cabinet Office inquiry team, led by civil servant Sue Gray, passed information to the force.

The gatherings, first reported by The Telegraph, took place on 16 April 2021 and went on until the early hours.

The prime minister's spokesman said it was "deeply regrettable that this took place at a time of national mourning".

Boris Johnson was not at either party - but he faces questions over alleged Covid rule-breaking at No 10.

The latest party revelations led to a backlash from opposition parties, who contrasted the behaviour of No 10 staff with pictures of the Queen sitting alone at the Duke of Edinburgh's funeral, due to Covid restrictions.