The number of alleged rule-breaking Whitehall parties has now reached 15 after the official who wrote the Covid rules admitted she failed to comply with them.

Kate Josephs, the former director of the government’s Covid taskforce, has apologised for holding an office drinks party when indoor socialising was banned.

She took to Twitter to say she is “truly sorry” for gathering with colleagues for alcoholic drinks in her office in the Cabinet Office to mark her leaving the civil service on December 17 2020.

Josephs, who describes herself in her Twitter bio as a “proud public servant”, is now the chief executive of Sheffield City Council.

The decision to hold a workplace gathering in Whitehall appeared to go against the official advice at the time.

According to The Telegraph, “dozens” of officials from the Cabinet Office’s Covid-19 taskforce attended the event, while the country was in lockdown.

Including Thursday’s revelations about two events involving drinks and dancing the night before the Duke of Edinburgh’s funeral – and the apparent purchase of enough wine to fill a suitcase – the total number of gatherings being investigated is up to 15.

On that same day, the government’s official Twitter feed replied to a query asking if employers could hold Christmas parties at the end of the working day.

It said: “Hi Mick, although there are exemptions for work purposes, you must not have a work Christmas lunch or party, where that is a primarily social activity and is not otherwise permitted by the rules in your tier.”

On Friday, Josephs tweeted a statement apologising for what happened.

She said: “As people know I previously worked in the Cabinet Office Covid Taskforce where I was director general from July 2020 to December 18, 2020.

“I have been cooperating fully with the Cabinet Office investigations and I do not want to pre-empt the findings of the investigation.

“However as chief executive of Sheffield City Council I am responsible for leading the organisation and working with partners across the city and region to support our covid response and recovery.

“That is why I have decided to make a statement.

“On the evening of 17 December, I gathered with colleagues that were at work that day, with drinks, in our office in the Cabinet Office, to mark my leaving the Civil Service.

“I am truly sorry that I did this and for the anger that people will feel as a result. Sheffield has suffered greatly during this pandemic, and I apologise unreservedly.

“The specific facts of this event will be considered in the context of the Cabinet Office investigation. I did not attend any events at 10 Downing St.

“I am grateful for the ongoing support of colleagues and partners and need now to ask that people allow the Cabinet Office to complete its investigation.

“I will not be able to respond to any further questions until the Cabinet Office investigation is complete.”

Sheffield City Council leader Terry Fox said the chief executive has discussed with him what happened and apologised face-to-face.

He said: “To be honest I need to express my deep disappointment – people will rightly feel angry and let down. I get that completely.

“After everything that Sheffield has been through during the pandemic, this is news that we did not want to receive.

“Over the last year, Kate’s been an asset to our city and she is working tirelessly for Sheffield and it’s people.

“Our residents will understandably have questions and concerns, and we await the findings of the investigation.”