Jack Monroe has started libel proceedings against Katie Hopkins over tweets the blogger claims caused “serious harm” to her reputation.

Monroe, a food writer and poverty campaigner, is suing the controversial Mail Online columnist over a dispute which dates back to 2015. Monroe alleges Hopkins posted tweets which implied Monroe defaced or condoned the damage of a war memorial and this resulted in death threats.

The High Court hearing, which started on Monday, originates from a series of public Twitter messages exchanged between the pair after a war memorial in central London was vandalised with the words “F*ck Tory scum” during an anti-austerity demonstration.

New Statesman contributing editor Laurie Penny shared an image of the graffiti, writing: “I don’t have a problem with this. The bravery of past generations does not oblige us to be cowed today.”

Hopkins, a former Apprentice contestant who has risen to fame for her inflammatory, anti-immigrant views, then sent a tweet to Monroe’s account, saying: “Scrawled on any memorials recently? Vandalised the memory of those who fought for your freedom. Grandma got any more medals?”

The court was informed Hopkins had mistaken Monroe for Penny – both commentators have been outspoken critics of the Tory party’s austerity policies.

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Quickly after Hopkins’s original message, Monroe wrote back: “I have NEVER ‘scrawled on a memorial’. Brother in the RAF. Dad was a Para in the Falklands. You’re a piece of sh*t.”

Monroe, who is reportedly seeking £50,000 in damages, later sent a second message demanding Hopkins apologise: “Dear Katie Hopkins, public apology and £5K to migrant rescue and I won’t sue. It’ll be cheaper for you and v satisfying for me.”

Hopkins deleted the first tweet but, said William Bennett, acting for Monroe, told the judge, Mr Justice Warby Hopkins “did not apologise or retract the allegation even though she knew it was false”.

Shortly afterwards, Hopkins said: “Can someone explain to me – in 10 words or less – the difference between irritant @PennyRed and social anthrax @MsJackMonroe.” Monroe’s lawyers claim that this second tweet bore a “defamatory innuendo meaning” that Monroe “approved or condoned the criminal vandalization of the women’s war memorial during an anti-government protest”.

Mr Bennett told the court: "The claimant's primary case is that by reason of the seriousness of the allegations and the scale of publication, serious harm to reputation has been caused.

"A widely published allegation that someone has either vandalised a war memorial or approved of such an act will inevitably cause serious damage to reputation."

Mr Bennett also said: "The libel was a particular affront to her because part of her identity is as a member of a family closely involved with the armed forces".

The blogger told the court that Hopkins’s messages had sparked abuse on Twitter, including death threats.

Jonathan Price, for Hopkins, told the judge in written argument that Hopkin’s case was that "this relatively trivial dispute arose and was resolved on Twitter in a period of several hours".

He argued "no lasting harm and certainly no serious harm", to Monroe's reputation resulted from the saga. Mr Price said the columnist’s case was that "these proceedings are an unnecessary and disproportionate epilogue to the parties' otherwise forgotten Twitter row".

But Monroe, from Leigh-on-Sea, Essex, rejected Price’s suggestion that rather than the row being the worst thing the blogger had experienced on Twitter, it had in fact been the best thing because it had offered an opportunity to bring the proceedings.

Monroe told the court: "These proceedings have been a nightmare. It has been an 18-month, unproductive, devastating nightmare.

"I did not want to be here today. I have offered several times though my lawyer to settle these proceedings outside court. This is the last thing that I wanted to be doing."

Monroe rose to fame for the blog Cooking On A Bootstrap, which receives around 100 thousand unique hits per day. The site, which was previously called A Girl Called Jack, centred on cooking on a budget and the struggle of feeding Monroe’s son for just £10 a week. The blogger identifies as non-binary transgender and goes by singular they pronouns, rather than "he" or "she".

Hopkins left The Sun in 2015 after writing a column that compared migrants to “cockroaches" and "feral humans" and said they were "spreading like the norovirus". She became the victim of a petition calling for her to be sacked.

A representative for Monroe did not immediately respond to request for comment.