The head of Channel 4 has apologised to a former staff member for the organisation not properly investigating a “serious” allegation made against Russell Brand in 2009.

However, the broadcaster found “no evidence” that staff at Channel 4 knew about the accusations made by four women in a Dispatches documentary before it was aired in September.

The 48-year-old was accused of rape, assault and emotional abuse as part of the joint investigation, also undertaken by the Times and Sunday Times.

Brand has denied all accusations, which relate to the period when he was at the height of his fame between 2006 and 2013.

He recently told the former Fox News host Tucker Carlson in a YouTube video that the claims were “very, very hurtful”.

Channel 4’s chief executive, Alex Mahon, said: “While the investigation did not find any evidence to suggest that any Channel 4 employees were aware of Russell Brand’s alleged behaviour contained in the programme, it did find that one former Channel 4 employee made a serious and concerning allegation about Russell Brand in 2009.

“This was not escalated to Channel 4’s then senior management team, nor investigated as it should have been. I have apologised on behalf of the organisation to the individual for this breakdown and for the distress this matter has caused.”

Mahon also said: “I commend the journalists involved in reporting the allegations and the people who have bravely come forward. Channel 4 has reported on itself without fear and investigated our own historical corporate responsibility thoroughly.

“While there is always more to be done, I am confident about the changes that have taken place in our industry over recent years, and it should now be clear that inappropriate and offensive behaviour has no place in it. I hope these issues can ultimately lead to further positive change.”

A report, released by Channel 4 on Thursday, found there was “no evidence” that Brand’s alleged behaviour on the Channel 4 shows Big Brother’s Big Mouth and Kings of Comedy, between 2004 and 2007, was known by staff.

“No evidence was found to substantiate the allegation in the [Dispatches] programme that Russell Brand’s behaviour had been discussed in a commissioning meeting in 2014,” it said.

Two reports were made to the Channel 4’s Speak Up facility after the Dispatches programme Russell Brand: In Plain Sight was broadcast.

A staff member made a report more than a decade ago about Brand’s conduct towards them, the report said, but this was “not passed up Channel 4’s senior management chain, nor investigated as it ought to have been in accordance with the procedures in place at the time”.

“Channel 4 also acknowledges delays in its ongoing communications with the former employee in 2023 due to the length of its investigation,” the report added.

Another anonymous report with “limited information” was not “substantiated”, the investigation said.

The report also examined what was known by “senior levels” at the broadcaster when Brand was a contestant on The Great Celebrity Bake Off: Stand Up to Cancer, which was filmed in 2018 but not broadcast until March 2019.

The programme Russell Brand: In Plain Sight was commissioned in December 2019.

The report said “the recollections of former and current Channel 4 staff interviewed varied about when concerns around Russell Brand started to circulate within the commissioning team” but that there was no written evidence or reports to Channel 4 about his casting before or after the Bake Off special aired.

The chair of Channel 4, Sir Ian Cheshire, said: “The board and ethics committee are confident that strengthened safeguarding processes introduced in the past decade mean that an allegation such as this would today be reportable through multiple routes.

“The investigation’s recommendations, which are accepted in full, will further strengthen Channel 4’s already rigorous safeguarding processes to further protect and uphold the welfare of all employees and those that the channel works with.”

After the journalistic investigation, complainants came forward to the BBC and the Metropolitan police.

Last year the corporation launched a review into the behaviour of Brand, who worked on BBC Radio 2 and BBC 6 Music programmes from 2006 to 2008.

In September, YouTube blocked Brand from receiving advertising revenue, and his Bipolarisation tour dates were postponed.

Programmes featuring him were also removed by Channel 4, and some episodes were taken off BBC iPlayer.

Brand, who was in the comedy films Forgetting Sarah Marshall, Arthur and Get Him to the Greek, has continued to publish content on the online video platforms Rumble and YouTube.

He has also denied allegations of controlling, abusive and predatory behaviour.