''The Department of Health will be investigating quite rightly to understand how this was able to happen," UK Northern Ireland Secretary Brandon Lewis told the BBC.

''We have got to be concerned about the fact that someone was able to secure a recording from inside a government building… We have to understand how that happened and how we deal with that,'' he said.

'The Sun' newspaper, which had published images of the illicit kiss that broke the COVID-19 lockdown rules in place at the time in early May, said the images came from ''a concerned Whitehall whistleblower''. Hancock issued an apology for breaking the rules on social distancing with someone outside his household bubble on Friday, which was accepted by Prime Minister Boris Johnson who backed him to stay on as a Cabinet minister. But his position as Health Secretary soon became untenable as not only the Opposition but even his own Conservative Party colleagues began speaking out against his actions, saying they undermined public trust in the lockdown rules.

''Those of us who make these rules have got to stick by them,'' Hancock said in his resignation on Saturday, as he promised Johnson his full support as a backbench Tory MP.

According to UK media reports, he had ended his 15-year marriage to wife Martha on Thursday – after he knew his affair with his close friend and aide was to hit the headlines on Friday. Both Hancock and Coladangelo are married with three children each. The pair are now believed to be separated from their respective spouses and plan to start a new life together.

Meanwhile, Javid praised his predecessor for all that he had achieved in the fight against the pandemic as he stepped into his new role back on the Parliament frontbench with a pledge to return the UK back to normal "as quickly as possible".

''I was honoured to take up this position. I also know that it comes with huge responsibility, and I will do everything I can to make sure that I deliver for the people of this great country," Javid told reporters on Sunday.

''We are still in a pandemic and I want to see that come to an end as soon as possible, and that will be my most immediate priority to see that we can return to normal as soon and as quickly as possible,'' he said.

The Pakistani-origin Conservative Party MP, who has previously held senior posts of Home Secretary and Chancellor in the UK Cabinet, returns to the frontline after he abruptly left government in February last year, a month before he was due to deliver his first Budget as Chancellor. At the time, he had clashed with Johnson's close aide, Dominic Cummings, over a plan to merge the offices of the Prime Minister and Chancellor – Number 10 and 11 Downing Street – closer together. Javid had disagreed with the move strongly and chose to step down before Rishi Sunak was appointed as Chancellor.

Cummings, now a deeply critical former Downing Street aide, took to Twitter to reignite his old feud with Javid with sharp criticism of his appointment as Health Secretary, implying that the decision was influenced by Johnson's wife Carrie – who is said to be close to Javid.