Hancock, 42, wrote to Prime Minister Boris Johnson to resign after The Sun newspaper published photos on Friday of the married minister embracing a woman who he had appointed to a taxpayer-funded role to scrutinise the performance of his department.
Hancock has been at the centre of the government’s fight against the pandemic, routinely appearing on the television and radio to tell people to follow the strict rules to contain the virus.
His departure means Johnson will have to appoint a new minister to take on the huge department that is responsible for overseeing the health service and tackling the virus, at a time when cases have started to rise again.
Johnson had said on Friday he had accepted an apology from the minister and considered the matter to be closed, but Hancock had faced rising pressure to quit.
“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,” Hancock said in his letter.
Johnson said in reply that he was sorry to receive it.
“You should be immensely proud of your service,” he wrote. “I am grateful for your support and believe that your contribution to public service is far from over.”
The Sun showed Hancock kissing the aide in his office last month, at a time when it was against the rules for people to have intimate contact with a person outside their household.
The opposition Labour Party also questioned whether he had broken the ministerial code: the woman, a long-time friend of Hancock’s, was appointed as a non-executive director, on a taxpayer-funded salary, to oversee the running of his department.
Labour leader Keir Starmer said on Twitter that Hancock was right to resign. “But Boris Johnson should have sacked him.”
With 128,000 deaths, Britain has one of the highest official death tolls from COVID-19 in the world and Hancock, in the post for almost three years, had been heavily criticised for his initial handling of the pandemic.
However Johnson’s Conservative government has been boosted by a rapid rollout of the vaccine programme, with 84% of adults having one dose and 61% having both, well ahead of most other countries.