The chief executive of Sheffield City Council has said she is "truly sorry" for going to a leaving party in December 2020 to mark the end of her role as Director General of the Cabinet Office's COVID-19 Task Force.
In a statement posted on Twitter, Kate Josephs said that on 17 December 2020, she "gathered with colleagues that were at work that day, with drinks," in their Whitehall office to mark the end of her tenure as head of the Task Force.
The COVID-19 Task Force is responsible for coordinating the Government's response to the pandemic. As part of its role, it provides support and advice to the Prime Minister, including data and analysis, and co-ordinates the Government's collective response.
At the time of the gathering, London was in Tier 3, meaning residents were instructed not to mix households indoors or in "most outdoor places". Hospitality was also shut.
Two days later, on 19 December, the Prime Minister announced that London, the South East and the East of England were to be moved into Tier 4, which saw all non-essential retail closed and guidance for people to stay home.
In her statement, Kate Josephs said: "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."
She added: "I am truly sorry that I did this and for the anger that people will feel as a result. Sheffield has sufferred greatly during this pandemic, and I apologise unreservedly."
The details of the gathering are to be considered in the context of the Cabinet Office investigation into the allegations of a number of parties held at Downing Street while the UK was in lockdown.
Josephs said she did not attend any events at 10 Downing Street.
She added: "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."
The leader of Sheffield Council, Cllr Terry Fox, expressed "deep disappointment," in response to the admission.
Cllr Fox said: "Kate has made a statement today about a gathering that happened in the Cabinet Office last year. I have discussed this in person today with Kate on a one-to-one and she has said sorry.
"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."