Paul Nuttall's press officer has resigned following the growing controversy over claims he lost friends in the 1989 Hillsborough disaster.
Lynda Roughley released a statement saying she was resigning from her position in the Ukip leader's team.
She took full responsibility for claims on Mr Nuttall's website that he had lost "personal friends" in the disaster where 96 Liverpool fans were trampled or suffocated to death in the away stands at Hillsborough football stadium in Sheffield.
She said: "Paul is a man of great integrity and would not say something he knew to be untrue. It's me who has made this mistake, and one I feel absolutely terrible about.
"I am frankly mortified at the distress this issue has caused Paul and may have caused to anyone involved with the Hillsborough tragedy.
"I have today offered my resignation, I could not be more sorry."
It comes after days of mounting controversy surrounding Mr Nuttall, who is running as the party's candidate in the Stoke-on-Trent by-election on Thursday, after he denied claims that he was lying about having been at Hillsborough.
Mr Nuttall repeatedly insisted he had been a survivor of the tragedy but the Hillsborough Families Support Group said they had had no recollection of saying he was present or offering to help in their long fight for justice.
His school at the time, Savio high school in Bootle, Liverpool, said they believed they had been made aware of all the identities of every boy who had been at Hillsborough in order to help them through the grieving process but the politician, who was 12 at the time of the disaster, was not one of them.
The 40-year-old said only "scum of the earth" would suggest his claims were not true and submitted two statements to the Guardian from his father and a Ukip staff member present during the disaster, saying he was there. But, according to the Guardian, his father's statement gave an incorrect age for him at the time of the disaster.
During an interview on Radio City Talk in Liverpool on Tuesday he was also challenged over the claim he had lost friends in the disaster as the statement appeared on his website.
Mr Nuttall was forced to admit the claim was false and he had "lost someone he knew" instead.
He told presenter Dave Eason: "I haven't put that out, that is wrong."
He later released a statement: "This was an article that I did not write and did not see prior to it being posted by a member of my staff," he said.
"Of course I take responsibility for those things that are put out under my name, but I was genuinely taken aback when this claim was brought to my attention and am both appalled and very sorry that an impression was given that was not accurate."
The claim was made in a 2011 blog post on his website echoing calling for a public inquiry into the disaster where he said: "Without them being made public we will never get to the bottom of that appalling tragedy when 96 Liverpool fans including close personal friends of mine lost their lives.”
The chairwoman of the Hillsborough Family Support Group, Margaret Aspinall, told LBC Mr Nuttall's claims were an "insult" to those who really did lose love ones that day.
She said: "A lot of people who were there that day did lose close personal friends and I think it's an insult to them as well as to all the families who did lose somebody on that day."
The Hillsborough claims are the latest allegations of lying made against the MEP.
Earlier this month he was also accused of falsely stating he lived in Stoke after Channel 4 News went to the home registered on his nomination papers and found it was empty with no furniture.
The Electoral Commission guidelines for candidates say those standing in Westminster elections must give their current home address on nomination papers. Mr Nuttall is currently being investigated by police for possible electoral fraud.
Mr Nuttall said he had been forced to move out of the house due to threats to his personal safety.
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