British former finance minister Sajid Javid will replace Matt Hancock as the country's health minister, Prime Minister Boris Johnson's office said on Saturday.

Javid resigned as Finance Minister last year after he refused to fire his political advisers as demanded by Johnson.

Matt Hancock quit on Saturday after he was caught breaking COVID-19 rules by kissing and embracing an aide in his office, enraging colleagues and the public who have been living under lockdown.

In the latest scandal to rock a government that has overseen one of the highest official death tolls from the pandemic, Hancock wrote to Prime Minister Boris Johnson to resign, saying he had let people down.

An increasing number of his fellow Conservative lawmakers had privately called for him to go after the Sun newspaper published photos on Friday of the married minister embracing a woman whom he had appointed to a taxpayer-funded role to scrutinise his department.

"Those of us who make these rules have got to stick by them and that's why I've got to resign," the 42-year-old said in a video on Twitter.

Hancock had been at the centre of the government's fight against the pandemic, routinely appearing on television to tell people to follow strict rules and to defend his department against criticism of its response to the crisis.

Javid was forced out of the Treasury in early 2020 when he lost a power battle with Johnson's then most senior ally, Dominic Cummings.

He will be tasked with helping the state-run health service recover from the pandemic and to deal with any future infection waves. Cases have started to rise in the last month.