More than 200 demonstrators have pledged to protest outside the Oxford Union on Thursday ahead of a planned evening appearance at the university’s prestigious debating society by Marine Le Pen, the leader of France’s far-right Front National.

“The union must reverse the decision to invite this notorious Islamophobe,” Weyman Bennett, joint national secretary of Unite Against Fascism, said on the group’s Facebook page. Referring to le Pen’s father, he added: “Jean-Marie le Pen once called the Holocaust a ‘detail of history’. We will demonstrate to argue that fascists should never be allowed a platform.”

Le Pen, who was greeted by similar protests when she addressed the Cambridge Union in 2013, took over from her father as head of the nationalist, anti-immigrant Front National in 2011 and has since spearheaded a campaign to detoxify the party, which finished last year’s European elections as France’s largest with more than 25% of the vote.

More than 300 Oxford professors, students, councillors and residents have also signed an open letter urging the union to rescind its invitation to Le Pen, saying Oxford was a multicultural city and that by inviting her, the union was “contributing to a climate of Islamophobia which only encourages racists and fascists.”

Lisa Wehden, this term’s union president, told the Oxford Student newspaper the union was a politically neutral institution that believed in the principle of freedom of speech, and an invitation to speak was “not an endorsement of any particular agenda. We invite no speakers who do not accept the right of our members to question them”.

A steady series of electoral gains has left the Front National with MPs, senators and several new mayors around France, and le Pen will be a key figure in the country’s next presidential election race. One recent poll showed she could win as much as 31% of the vote in the 2017 election’s first round, although it is predicted that she would lose the second round to any of the other main contenders including President Francois Hollande.

In the wake of last month’s Paris terrorist attacks that left 20 people dead, including three Islamist gunmen, Le Pen called for a return of the death penalty, surveillance in mosques, and the reintroduction of national service for boys and girls. “We must not be silenced … We must not be scared of saying the words: this is a terrorist attack, carried out in the name of radical Islam,” she said.