Boris Johnson attended leaving do during strict January lockdown

Boris Johnson attended a prosecco-fuelled leaving do for a No 10 aide during the strict post-Christmas lockdown, which is now under police investigation, the Guardian has learned.

Sources said the event was held in Downing Street in part as a leaving do for a senior policy adviser who is now a top civil servant working in the Department for Digital, Culture, Media and Sport.

Prosecco is alleged to have been drunk by some staff, with Johnson understood to have given a speech thanking the official for their work and staying for around five minutes.

It was reported in the Daily Telegraph that Johnson was seen going up to the flat on the night in question, where Abba songs including The Winner Takes It All were played. No 10 did not deny Johnson was present at the flat gathering.

Downing Street was again forced into a U-turn on Tuesday, having initially refused to confirm whether it would reveal any fixed penalty notice that is issued to Johnson by police for breaching Covid rules.

Government insiders have not been told how long the police investigation could take but hope it will only be a matter of weeks given the substantial evidence gathering already done by a Cabinet Office team of around half a dozen people.