When Ann Widdecombe was unveiled as the Brexit party’s surprise European election candidate, the tactical aim was clear – show Conservative voters that switching their vote to Nigel Farage’s new outfit made so much sense that even former ministers were happy to do so. Widdecombe’s name recognition is still high even in semi-retirement, and the move is embarrassing for a Conservative party struggling to fight an election it never wanted.

The anti-Brexit campaign group Led By Donkeys responded by posting billboards featuring Widdecombe’s face, the quote “homosexual acts are wrongful” in giant letters, and was headlined “Target gay people”. The aim was to warn voters of Widdecombe’s hardline beliefs, and by extension the views of the new party’s potential MEPs. And there was a small disclaimer at the bottom attempting to contextualise the comments.

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But the poster was fundamentally flawed – missing the fact that most people would, in passing, simply see billboards plastered with homophobic messages. After a social media backlash, Led By Donkeys apologised and agreed to remove the posters.

We live in a climate where homophobic violence and abuse is common, and publicising such statements in a manner that fails to challenge them, or, worse, could be seen as condoning the sentiments, is intensely dangerous. For the campaign to have real impact, Widdecombe would need to be made uncomfortable by the unearthing of those views – and she is not. She has been consistently open about her intolerance.

Facebook Twitter Pinterest A Led By Donkeys banner in Parliament Square, London, during the Put It To The People march. Photograph: Jiri Rezac/Led By Donkeys

And more than that, the Brexit party is a single-issue party designed to attract votes as a protest, and use its popularity as proof that the public want a hard Brexit. Very few voters will change their mind about voting for Nigel Farage et al because they’re pro-Brexit but anti-homophobia.

The Widdecombe posters are coming down, but other Led By Donkeys billboards featuring Farage, Boris Johnson and Jacob Rees-Mogg remain. Similar problems lie here too: if the people targeted don’t feel embarrassment or shame for their chosen statements, and there’s no evidence any of them have, then you’re simply spending large sums of money to publicise their views across the country. The crowdfunded campaign has so far raised almost £450,000 yet doesn’t appear to have elicited much annoyance from the targeted politicians, or changed many minds.

The previous campaign from the same group involved a series of giant tweets. The ads blasted Farage and prominent Brexiters for misleading the public. But none of the quotes had actually been tweeted by the people they were attributed to: instead the comments were taken from speeches, written articles, Hansard or interviews. It was an own goal that enabled their political opponents to dismiss them.

That the group, and other remain campaigns too, fall into the same traps ultimately stemming from the fact that they appear aimed at voters who are ardently pro-EU, rather than at Brexit sympathisers who may be willing to switch.

The Farage billboards only appear as a gotcha to those who would never consider voting for him anyway. The Widdecombe posters flattered certain liberal sensibilities and pandered to a sense of moral superiority among remainers. Spending just shy of half a million pounds to publicise the beliefs of hard-right politicians can only boost those candidates. There’s a thin line between mockery and endorsement.

• Dawn Foster is a Guardian columnist