The government will investigate how the footage of Matt Hancock kissing an aide in his office that triggered his downfall ended up in the public domain, a cabinet minister said. Brandon Lewis, the Northern Ireland secretary, said the Department of Health and Social Care (DHSC) would undertake an internal investigation into the leaking of the CCTV pictures to the Sun. Multiple media reports have said a DHSC employee was the culprit. The tabloid’s publication of footage recorded on 6 May by the CCTV in Hancock’s office of him embracing Gina Coladangelo led to the health secretary’s resignation on Saturday and replacement by Sajid Javid, the former home secretary and chancellor. Lewis’s remarks came amid claims the leaker had sought the help of an anti-lockdown campaigner in placing the pictures with a media outlet in order to undermine Hancock. As health secretary, Hancock was one of the key ministers arguing last autumn that a second lockdown was needed to reduce Covid infections and stop the NHS becoming overwhelmed. Speaking on Sky News’s Trevor Phillips on Sunday, Lewis said: “I have seen some of the reports this morning outlining how different journalists think the tape might have got out there. That is certainly a matter I know the Department of Health will be looking into to understand exactly how that was recorded, how it got out of the system. It’s something we need to get to the bottom of.” The security and privacy of government business means ministers need to understand how someone was able to access and record the footage and then share it with a newspaper, he said. “What happens in government departments can be sensitive, important and people need to have confidence that what is happening in a government department is something that allows government to be focused on these core issues, and the sensitivity sometimes in the security sense of those core issues. “I do know that is something the Department of Health will be taking forward as an internal investigation and we need to see and let them have the space to do that, to understand how this happened and to ensure this kind of situation can’t happen again or across government indeed.” The status and nature of the health department’s investigation is unknown, as is whether its findings will be made public. The Guardian reported on Friday that Downing Street had ruled out a full-scale leak inquiry, despite the security implications of the footage going public, amid concern that, if identified, the leaker could present themselves as a whistleblower who was exposing wrongdoing and thus claim the legal protections whistleblowers are meant to enjoy. Sources say that remains the case. The Mail on Sunday reported that the leaker sent messages via Instagram to the unnamed anti-lockdown activist. One said: “I have some very damning CCTV footage of someone that has been recently classed as completely f***ing hopeless. If you would like some more information please contact me.” That was reportedly sent on 17 June, the day after Boris Johnson’s former chief adviser Dominic Cummings published text message exchanges he had with the prime minister last year in which Johnson called Hancock “totally fucking hopeless”. A second message, sent on 19 June, said: “I really need to be careful with this but it involves him in a very compromising position with some [sic] who isn’t his wife last month.” And a further message, sent later that day, added: “I have the full video … it’s now been deleted off the system as it’s over 30 days.” The Guardian asked the DHSC for further details of its inquiry and the Mail on Sunday’s claims.