A Rotherham businessman is suing a former UKIP official over a tweet accusing him of child grooming.
Zahir Monir, of Rotherham, is suing Steve Wood, the ex-chairman of UKIP's Bristol branch and who stood for Bristol South in the 2015 general election.
In a hearing at London's High Court, Mr Monir's counsel, Julian Santos, claimed that the allegation, three days before the election, was 'as serious as it gets' and republished on a 'massive' scale.
He told Mr Justice Nicklin: "This was an appalling and shameful tweet which Bristol UKIP should never have published, should immediately have deleted and should have been at pains to apologise for.
"The defendant, as chairman of this organisation, should equally have been at pains to apologise."
Mr Santos said that to dismiss the tweet as 'merely unattractive and regrettable' and to argue that it had not caused serious harm to Mr Monir's reputation aggravated the injury caused.
Mr Santos said that being branded a 'paedophile' had a devastating impact on Mr Monir who, until then, had spent his life involved with charities and helping young people.
It had been devastating for his family and Mr Monir had been diagnosed with depression, the court heard.
His property had been egged and a brick thrown through a window, while he had been called 'Jimmy Savile' by another parent at the school where he was previously a parent governor.
David Hirst, counsel for Mr Wood, who runs an enforcement business, called the claim for damages and an injunction 'most unmeritorious.
He said that Mr Wood, chairman at the time, was not responsible for publication of the tweet, which was composed and activated by vice-chair John Langley.
He had no involvement in or knowledge of it.
Mr Hirst disputed that the tweet alleged Mr Monir was guilty of child-grooming, saying the words meant that there were grounds to suspect.
He said that Mr Monir had not demonstrated that the tweet, which was published to followers of a local political party in south-west England, was read by persons able to identify him.
Mr Wood immediately deleted the tweet when notified of it, conveyed his apologies to Mr Monir and had always considered it inappropriate and regrettable, he added.
The hearing is expected to last five days with a ruling given at a later date.