Ms Pinder, a trained chef who co-wrote a recipe book, posted that the pair were celebrating, days after she became engaged. 

Last year, she was pictured leaving through the front door of No 10 having been one of 30 guests at a party in the Downing Street garden to celebrate Mrs Johnson’s marriage to the Prime Minister earlier that day.

People told to ‘limit social contact’

Three days before Ms Pinder posted the photograph with Mrs Johnson on her Instagram account, the Prime Minister tightened Covid-19 restrictions in response to the rising transmission of Covid-19.

A statement issued by the Government on September 9, when the new rules were announced, warned: “This is not the time for complacency; we have seen big increases in the spread of the virus in Europe and other countries.”

The statement said it was “critical that everybody observes the following key behaviours”.

Speaking at a Downing Street press conference on September 9, Mr Johnson said: “If we are to beat the virus then everyone, at all times, should limit social contact as much as possible and minimise interactions with other households.

“It is safer to meet outdoors and you should keep your distance from anyone you don’t live with, even if they are close friends or family.

“By bearing down on social contact and improving enforcement, we can keep schools and businesses open.”

On September 7, Matt Hancock, then the health secretary, warned that the recent increase in transmission was “among more affluent younger people”.

Mr Hancock later quit his post after leaked images showed the MP in a clinch with an aide in his ministerial office. 

He was accused of breaching social distancing guidance and said: “We owe it to people who have sacrificed so much in this pandemic to be honest when we have let them down as I have done by breaching the guidance.”