Two Ukip chairmen in Merseyside have resigned in protest at the “crass insensitivity” of Paul Nuttall’s handling of the controversy over his claims about the Hillsborough disaster.

Adam Heatherington and Simon Monkcom handed in their resignations from the party this week, following their leader’s admission earlier this month that claims on his website about losing close friends in the Hillsborough disaster were false.

Victims’ families reacted with dismay. Margaret Aspinall, chair of the Hillsborough Family Support Group, whose 18-year-old son James died in the disaster, described it as “appalling”.

The resignations will come as a blow to Nuttall days before he attempts to unseat Labour in the hotly contested Stoke-on-Trent Central byelection on Thursday.

In 2012, Heatherington became the youngest candidate to stand for elected mayor in Liverpool.

Monkcom, chairman of Nuttall’s own branch, Ukip Liverpool, said: ‘Although the timing of our resignations is unfortunate in light of upcoming elections, both Adam and I wish to make it clear, where the painful subject of Hillsborough is concerned, with closure not yet in sight, this unprofessional approach and crass insensitivity from high profile people closely within and without Ukip is upsetting and intolerable.

“We identify most strongly with all the good people of Liverpool and most importantly the families of the Hillsborough victims who have fought so hard and long for justice, in their condemnation of the way Ukip has handled these issues and have resigned our positions and membership of Ukip forthwith.”

Heatherington added: “We have been affected both personally and professionally by words that were not said in our name. With this in mind, we wish to apologise to the people of Liverpool and the Hillsborough families for any offence caused and have done what we consider to be the only honourable thing we could do which was to resign and disassociate ourselves from Ukip. I felt that supporting a libertarian party was the right thing to do in order to effect change within the political system in this country. Unfortunately that dream has been shattered and the potential of Ukip has been squandered by people who have demonstrated they are not fit to lead at present.

Nuttall first publicly claimed to have been at Hillsborough in a letter to the Liverpool Daily Post in July 2010. He raised the matter again in May last year, telling the BBC’s Politics Show North West that he had been in the overcrowded Leppings Lane end of the ground.

He told the programme he believed the police officers responsible for the disaster should be prosecuted. “I think people should carry the can for their actions,” he said.

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Paul Nuttall gets emotional at Ukip conference – video

Nuttall was 12 at the time of the disaster, and was a pupil at Savio high school in Bootle, Liverpool. One of his former teachers, a Roman Catholic priest, told the Guardian that the school believed it had been aware of the identities of every boy who had been at Hillsborough in order to help them through a difficult period, and that Nuttall was not among them.

A fellow pupil at the school who says he has been a friend of Nuttall for decades said the Ukip leader had never mentioned being there. “I have been very good friends with Paul for over 25 years,” he said, adding that during that time they had never spoken about Hillsborough.

While the teacher and friend expressed surprise that Nuttall had said he was at Hillsborough, their comments do not prove that he was not present.

Nuttall’s admission about the inaccurate statement on his website came in an interview with Liverpool’s Radio City News. The interview followed his denial that he had lied about being a survivor of the 1989 disaster, in which 96 Liverpool fans were killed at an FA Cup semi-final.

When the presenter, Dave Easson, who was at Hillsborough, the home of Sheffield Wednesday, on the day of the disaster, showed him the evidence that the claim had been made on his website, Nuttall replied: “I haven’t lost a close, personal friend. I’ve lost someone who I know.”

Nuttall maintains that he was at Hillsborough on the day of the disaster and has said only “scum of the earth” would suggest otherwise.

Ukip gave the Guardian two statements on behalf of Nuttall, one from his father and another from a Ukip employee, saying that they and Nuttall had been at Hillsborough on the day of the disaster, 15 April 1989. The statement from Nuttall’s father gave an incorrect age for his son at the time.

At the Ukip party conference in Bolton last week a visibly emotional Nuttall refused to answer questions from reporters asking him to prove he had been at Hillsborough and described the episode as a “smear campaign”.