BBC Radio 1 broke broadcasting guidelines when Lily Allen and Ed Sheeran swore on air at the Big Weekend festival, the watchdog Ofcom has said.

Allen swore six times during her performance at the station’s event in Glasgow in May, which was broadcast live between 17:30 and 18:00 BST.

Presenter Scott Mills warned listeners the sets may contain “strong language”.

But Ofcom ruled the offensive language was broadcast when “children were particularly likely to be listening”.

The BBC said there was an immediate apology after the broadcast.

It explained that a “comprehensive risk assessment” had been carried out and that singers were told not to swear in writing and on signs in their dressing rooms.

Ofcom noted that as Lily Allen was known to use strong language, “it was reasonably predictable that her set could contain the most offensive language”.

The BBC explained that it had considered cutting away from Allen’s set twice, but a senior producer decided to continue because apologies had been given and it was believed that not that many children would be listening.

It also stated that, in retrospect, Radio 1 should have stopped broadcasting Allen’s set live after the second song that contained offensive language and edited the rest of her performance.

Knowing there could be some swearing why didn’t the BBC simply go on delay?