One of Britain’s biggest bonfire festivals has been plunged into a fresh racism row after a child was blacked up for a costume contest before a parade through Lewes.

The boy, believed to be aged five or six, was taking part in a pre-bonfire night event with his mother, who is a member of the Lewes Borough Bonfire Society. For decades, the society has paraded through the East Sussex town in Zulu-style costumes and has been widely criticised for allowing blackface.

Campaigners said they were shocked at how the child was made up after a bitter dispute last year resulted in the society pledging to end the practice. The Lewes bonfire parade attracts up to 60,000 spectators and the town’s bonfire societies have about 6,000 members, who are part of an intense and sometimes insular culture.

A picture of the blacked-up child has been displayed in a photography shop in the high street in recent days and posted on Facebook, causing anger in the town, with some accusing the bonfire society of provocation, while diehard bonfire enthusiasts claim anti-racism campaigners are trying to wreck their traditions.

A spokeswoman for the activist group Bonfire Against Racism, expressing concerns that people may black up at the parade on Monday, said: “To dress a child in total blackface is manipulative – both of the child and the potential audience. It feels like a deliberately provocative act.”

Mick Symes, a member of the society’s committee, said the boy’s costume was against guidelines it drew up last year stating that less than half of any facial makeup should be black. The guidelines did not extend to wearing black body stockings.

“I profusely apologise. We slipped up and once is once too many. As a society we made quite robust changes last year and reinforced them at committee meetings in the run-up to bonfire,” he said.

Last year, the leader of a Yorkshire-based Zulu dance troupe originally from Durban in South Africa, which had been invited to join the procession, insisted it would not come unless blackface was dropped.

After delicate negotiations, the society agreed and said it would remove skulls, nose rings and dead monkeys from its costumes, which the troupe leader, Thanda Gumede, said were a “gross misrepresentation and unacceptable stereotype of Zulu and black people at large”.

Gumede had been booked to perform again in Lewes this year, but has cancelled in protest. He said he was upset that the child had been allowed to compete, and at others’ reactions.

“Online I saw people defending it and saying he was just carrying on a tradition. The reason I am upset is that as a black person I face a lot of racism. My greatest fear is that people get away with it and nothing is done,” Gumede said.

After making a stand last year, he said: “I didn’t expect I would be in a position where I would have to deal with blackface again.”

After the society had paraded through Lewes with a giant tableau of Kim Jong-un clinging on to the Empire State Building during the 2017 parade, its members gathered for a bonfire prayer and the society’s chairman ceremoniously placed a tin of “Zulux” paint on to the bonfire, to symbolise the end of blacking up.

Regarding the latest incident, Symes said when he saw the boy’s costume, he thought “oh, no. Not again.” Symes said he was at the contest, but the boy’s mother arrived early, there was no one else around and the boy’s face was partially covered by a beaded veil, obscuring the blackface. “It was one of those things where communication wasn’t as good as it should have been,” he said.

Some of the adults taking part in the warm-up competition held two weeks ago covered parts of their faces in white and red paint, as well as black, as per the society’s new policy, but campaigners argue this is still essentially blackface. Other Lewes bonfire societies dress as Native Americans, Vikings, Roman legionaries, Genghis Khan’s Mongol warriors, and monks.

A resident, who asked not to be named after his family was attacked for speaking out last year, said: “Bonfire is so locally entrenched that people who on any other day would say blackface is unacceptable are prepared to make an exception and say it is not racist, even though their black neighbours are saying it is offensive.

“There’s an expression in the bonfire societies, ‘We wun’t be druv’ [We will not be driven] and it is happening again now.”

Bonfire Against Racism said: “As Thanda explained last year, Zulu tradition includes a long history of body and face painting, but blackface is separate to this. Blackface is an offensive western caricature, as too are the nose bones, shrunken heads and skulls used in borough bonfire costumes.”