Communications watchdog Ofcom has said it will take no further action after a “very tired” Dermot O’Leary swore on live TV during his Comic Relief dance marathon.

The broadcaster, who recently left his job hosting The X Factor on ITV, raised more than £600,000 for good causes by dancing for 24 hours.

But 18 hours into his marathon effort, he greeted a friend outside New Broadcasting House in central London by saying: “how f***ing fantastic to see you”.

Dermot O'LearyDermot O’Leary raised a massive amount with his dance marathon (James Flood/Comic Relief)

Ofcom noted O’Leary apologised within a minute and the BBC broadcast a further apology shortly afterwards.

The BBC told Ofcom it had warned all its guests not to swear, adding that O’Leary was “aware he was wearing a live microphone and that the event was being broadcast live”.

The Ofcom report noted: “However, given the event had begun at 19:00 the previous evening and by the time of the incident at 13:30 the next day the BBC said Dermot O’Leary was very tired having been dancing for over 18 hours and throughout the night.”

The watchdog’s spokesman said: “After carefully investigating this programme, Ofcom took into account that the BBC had issued two apologies immediately after the offensive language was aired. As a result, we consider the matter resolved.”