Allegra Stratton has stepped down as the government’s spokesperson for the Cop26 climate summit after footage emerged of her joking about a party at Downing Street during the peak of lockdown rules in December last year. Boris Johnson told a coronavirus press briefing on Wednesday that Stratton had been an “outstanding spokeswoman … I am very sorry to lose her”. But he added: “I take responsibility for everything that happens in this government and I have throughout the pandemic.” In a statement sent to journalists and read out to TV crews in front of her home, Stratton – Johnson’s former press secretary – said she deeply regretted joking with other No 10 aides during a rehearsal for a later-dropped plan for filmed Downing Street press conferences. “The British people have made immense sacrifices in the battle against Covid 19. I now fear that my comments in the leaked video of 20 December may have become a distraction against that fight,” she said. “My remarks seemed to make light of the rules, rules that people were doing everything to obey. That was never my intention. I will regret those remarks for the rest of my days and offer my profound apologies to all of you for them.” Saying she remained proud of her work on Cop26, Stratton said: “I understand the anger and frustration that people feel. To all of you who lost loved ones, endured intolerable loneliness and struggled with your businesses – I am sorry and this afternoon I have offered my resignation to the prime minister.” Stratton moved to her Cop26 role after the planned Downing Street briefings were axed. A former journalist for the Guardian, BBC and ITV, Stratton also worked for the chancellor, Rishi Sunak, before switching to No 10. Earlier Downing Street said Stratton and another No 10 aide, Ed Oldfield, who was named in the video, had not been suspended. Oldfield has not offered any comment since the videos emerged. A number of senior journalists and former colleagues of Stratton said she was being scapegoated for a party which, during the video, she said she had not even attended. Nazir Afzal, a senior prosecutor who has been a vocal campaigner for the victims of Covid-19 after losing family, said: “I accept Allegra Stratton’s apology, but she was not the problem. A good leader doesn’t blame the staff. A good leader takes responsibility.” Robert Peston, ITV’s political editor, who had worked with Stratton while she was a journalist, said her resignation was confirmation the event had taken place. “She is a model for many in modern politics … in that she has taken responsibility and quit without prevarication. “It would be nonsensical for [Stratton] to have resigned if the Downing Street party had never happened, and she wasn’t conspicuously making light of it. So she has just blown up the prime minister’s ‘I’ve been assured the party never happened.’” Jo Goodman, co-founder of Covid-19 Bereaved Families for Justice, said it was hard to accept Stratton’s apology. “There was simply no way she could have stayed in the position after the pain and hurt her words have caused bereaved families over the past 24 hours,” she said. “If she’s truly sorry, she now needs to tell the full truth. That means coming clean on what happened, and who was there.”