The Government will be launching an internal investigation into how CCTV footage of Matt Hancock kissing an aide in his Whitehall office was leaked, a Cabinet minister has said.

Within 48 hours of being released, the unprecedented security breach resulted in Mr Hancock’s resignation as Health Secretary, after the footage showed him breaking Covid social distancing rules in early May.

The Department of Health and Social Care (DHSC) will seek to find out how the former health secretary came to be recorded in his office and how that footage became public, Northern Ireland Secretary Brandon Lewis said.

The Telegraph understands Mr Hancock had no idea the camera existed when it captured him kissing adviser Gina Coladangelo, and government sources said it was "unheard of" for cameras to be installed in ministers’ offices.

Asked on Sky News’ Trevor Phillips On Sunday programme about the leak, Mr Lewis said: "It’s something we need to get to the bottom of.

"Quite rightly what happens in Government departments can be sensitive and important.

"So, yes, I do know that is something the Department of Health will be taking forward as an internal investigation."

It comes despite Downing Street refusing to comment on Friday about whether a probe into the leak will be launched.

‘Completely unacceptable’ for ministers to be filmed inside their offices

It is the first time a Cabinet minister has been filmed in their own office without their knowledge.

Former Cabinet ministers Alan Johnson and Rory Stewart both said there had never been cameras in their offices during their time in government.

Alan Johnson told Trevor Phillips On Sunday: "I could never understand why there was a camera in the Secretary of State’s office.

"There was never a camera in my office when I was health secretary or in any of the other five Cabinet positions."

Mr Stewart, who was International Development Secretary from May to July 2019, said in a tweet: "I definitely did not know that there were cameras in any of my ministerial offices (in fact I was told – when I asked if there were any cameras – that there were not cameras in my office in DfiD)."

CCTV cameras can be seen positioned outside the Department for Health and Social Care, but this is the first time a Cabinet minister has been filmed in their own office without their knowledge

Credit: Geoff Pugh

He added: "If it were a departmental camera – perhaps focused on the door for security reasons – then it would be seen by the security officers.

"Someone else installing it would have some challenges – security passes, doors, access to ministerial offices etc."

Former health secretary Jeremy Hunt said that it was "completely unacceptable" that ministers were being filmed inside their offices and he added that the leak had "possibly" been a breach of the Official Secrets Act.

The chairman of the Commons Health Select Committee told The Andrew Marr Show: "It’s completely unacceptable from a security point of view that ministers are being filmed inside their own offices without their knowledge.

"And so there’ll be issues that our intelligence agencies will want to look at very, very carefully."

He added that there is an "another issue" – over ministers’ ability to have private conversations which would "enable them to make the right decisions" without being spied on.

The Henry Jackson Society think tank has reported the disclosure of the footage as a breach of the Official Secrets Acts to the Metropolitan Police, but the force said it considered the leak "a matter for the relevant Government department" rather than police.

The Sun claimed the footage was released by a whistleblower disgusted that Mr Hancock was breaking Covid rules while telling people to obey them, but it remains unclear how the video was captured and disseminated.