The 64-year-old rocker was joined by his band the Boomtown Rats as they headlined the Brentwood Festival in Brentwood last weekend (16-17Jul16).

The group is most famous for its song I Don't Like Mondays, but Bob's cursing led to hordes of guests leaving before the stars had the chance to perform the hit.

Bob started as he meant to continue, telling the crowd as he ran onto the stage: "We don't do Abba. We don't do Robbie f**king Williams."

After just one song, Bob stopped the music and addressed the audience, stunning many when he began criticising their dress sense.

"Brentwood, we are the Boomtown Rats," he shouted. "We are mega. And you are Brentwood. How do we know that you are Brentwood and we are mega? Because I am wearing a f**k off pretend snakeskin suit and (locals) are wearing f**k off cowboy shirts even though they live in London."

Referencing a member of his band, Bob continued: "This (guy), who you'll remember as a slim handsome young lad..., is wearing a f**k off purple suit with an elasticated waistband so that when he gets even f**king fatter you won't notice."

He then seemed to get confused about the event he was performing at, labelling it a "rock and roll festival" instead of the family event it was.

"On the other hand Brentwood, you are wearing wall to wall f**king Primark (British bargain clothing store)," he added. "This is a rock and roll festival. When you come to a rock and roll festival you dress for a rock and roll festival. You can never be too careful."

One attendee left with her husband before the Boomtown Rats finished their set, telling the Essex Chronicle newspaper: "We were just thinking we probably wouldn't bother staying when Bob launched into an extraordinary, expletive-laden rant.

"As he launched into another dreadful song, we, along with hordes of others, headed for the exit. All around you could hear mutterings from fed up festival-goers of how disgusting he was and 'how dare he'. It was a shame he had marred what was otherwise a fabulous day out."

Laurie Edmonds, who organised the event, told the publication that they had deliberately put the Boomtown Rats on the schedule after the watershed, as they are a "punk band", but apologised for the amount of swearing in Bob's stage chatter.

"We were disappointed that there was so much swearing. We want this to be a family event and it would have been nice if it was toned down," she said. "Some people who felt it was offensive made the decision to leave. We're truly sorry if people were offended. It wasn't our intention in booking them."