The civil servant who runs Boris Johnson’s private office is facing claims of involvement in another boozy gathering in Downing Street that may have broken lockdown rules.

Martin Reynolds, the principal private secretary to the Prime Minister, attended a gathering on the evening of December 18 2020, where aides stayed late and alcohol was consumed.

The event took place in the Downing Street private offices, where Mr Johnson’s inner circle of civil servants sit, on the same day as a controversial party of Number 10 press advisers.

Three Government sources told The Telegraph of the gathering. Some said wine was served and expressed surprise it had gone unreported, given the focus on the other event that day.

Lord Lister, then Mr Johnson’s chief of staff, who sat in the private office, also said alcohol was consumed at times there in the run-up to Christmas, while denying rules were broken.

At the time, the Government’s Covid rules forbade Christmas parties being held at work. The gathering took place on the last Friday before Christmas.

Downing Street did not deny that alcohol had been consumed on December 18 in the private office or that Mr Reynolds was in attendance at points.

However, a spokesman denied it was a party, saying those present had been staying late to work on Covid-19 rule changes to be announced that weekend.

A No 10 spokesman said: “A number of private office staff worked late into the evening on the Covid response.”