The UK's health minister Matt Hancock has resigned after he admitted breaking COVID-19 guidance by kissing and embracing an aide in his office, saying he had become a "distraction" to the vaccine program.

The government on Saturday published Hancock's resignation letter to Boris Johnson and the prime minister's response.

"We have worked so hard as a country to fight the pandemic," Hancock said. "The last thing I would want is for my private life to distract attention from the single-minded focus that is leading us out of this crisis."

In a video published on Twitter the health minister, who had been largely responsible for one of the most successful vaccine rollouts in Europe, recognized the sacrifices that members of the public have had to make in order to adhere to social distancing rules. He went on to admit his failure to abide by the same guidance had led to his resignation. 

Opposition leader Keir Starmer, who had avoided joining calls for Hancock's resignation in February when the UK's High Court ruled the health ministry had unlawfully failed to publish details of COVID-19-related contracts, was not so conciliatory this time around. Taking to social media, Starmer wrote Hancock was right to resign but that Boris Johnson should have sacked him first.

Despite his admission, Johnson praised Hancock for his work in leading the response to the COVID-19 pandemic. 

"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."

Former finance minister Sajid Javid returns to the cabinet as the new health minister just 16 months after he had resigned after refusing to sack his aides in a row with Johnson.

Johnson has been criticized for his loyalty to Hancock and had originally said the matter was closed on Friday following pictures of the health minister kissing and embracing Gina Coladangelo, a friend he hired last year, were splashed on the front page of The Sun. Coladangelo has also left her role at the ministry of health and social care, according to several UK newspaper reports.

Picture source unclear

The health ministry will launch an internal investigation into how the footage recorded inside Hancock's office made its way to a national newspaper.

The Sun said the picture of Hancock, who is married, and the aide, Gina Coladangelo who is also married, was taken last month. The images have not been independently verified. 

The daily newspaper did not say how it obtained the security camera images, but it cited a whistleblower as commenting on the relationship.

The Sun said the two had known each other since they were both at Oxford University in the early 2000s. She was listed on the health department's website as a non-executive director.