A Reform UK mayoral candidate has described members of a Jewish neighbourhood watch group as “cosplayers” and likened them to “Islamists on horseback” in comments made after an attack on ambulances run by a Jewish charity.

Chris Parry, who remains Reform’s mayoral candidate for Hampshire despite a previous controversy in which he said David Lammy should “go home” to the Caribbean, made the comments on Monday about Shomrim, a group of volunteers who safeguard communities including Orthodox Jewish families.

Parry, a retired rear admiral, retweeted a post on X by Catherine Blaiklock, a co-founder of the Brexit party, hours after news of the attack on the ambulances in north London emerged.

Shomrim works alongside Hatzola, the charity ambulance service that was targeted by arsonists early on Monday morning and provides emergency medical response and transportation to hospitals for both Jewish and non-Jewish people.

Police said on Monday that counter-terrorism officers were leading an investigation into the arson attack on four ambulances.

“Can Christian’s [sic] in Britain set up their own police and patrol certain neighbourhoods?” said Blaiklock, who posted a picture of a number of Shomrim vehicles.

Parry shared the post, adding: “Remember that these cosplayers have no more jurisdiction or legal authority than ordinary citizens.”

When he was challenged over the original post’s characterisation of Shomrim, Parry replied: “They are a community organisation, not a legal entity. It’s the same with Islamists on horseback. But if it offends you, I’ll remove it.”

The politician, who is set to stand in Hampshire and the Solent in 2028, apologised for his “clumsily worded” post on X about Lammy in January. He had said the deputy prime minister, who was born in London to Guyanese parents, should “go home to the Caribbean” where his “loyalty lies”.

Contacted by the Guardian about his comments on Shomrim on Monday, Parry said: “Most people on X commenting seem to be confusing various community action groups with the real police. Keen that people understand that.”

Rabbi Herschel Gluck, the president of Shomrim, described Parry’s comments as “ignorant” of the work that the organisation carried out.

“It shows a level of bias and ignorance which I’m surprised at given that this is a politician who aspires to be a mayor. These types of comments are deeply strange, to put it mildly,” Gluck said. “We work on a voluntary basis with all sections of the community and have a very close relationship with the police, who are very appreciative of our role.”

He added that Shomrim volunteers were currently on higher alert in the wake of the arson attacks at the weekend and had stepped up patrols.