As she surges to new heights in opinion polls, the National Front leader Marine Le Pen has threatened to sue journalists who describe her party as far right.

“They put us in the same bag as [mass murderer Anders] Breivik and [the Greek neo-Nazi party] Golden Dawn. They shake up the bag and try to give us a filthy image,” Ms Le Pen said.

From now on, she warned, she would sue any journalist who waged “linguistic war” on her party. It is not just her cleaned-up version of the National Front which should never be described as far right, she said. She claimed – against the historical record – that the “nationalist” party founded by her father 41 years ago had never had links with the extremes of fascism or Nazism.

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French newspapers and Socialist politicians immediately rose to Ms Le Pen’s challenge yesterday. Thousands of people joined in a Twitter campaign, started by a Socialist MP, to declare: “The National Front and Marine Le Pen are far right”.

In a front page editorial, the centre-left newspaper Le Monde said: “Let’s state it again clearly. By its position on the chess-board of French politics, in its ideas and its policies, the National Front is, today as yesterday, a movement of the extreme right.”

The centrist newspaper Le Parisien traced the origins of the National Front in the early 1970s to a coalition of anti-state populists, Catholic fundamentalists, neo-fascists, former SS members and Nazi collaborators.

Ms Le Pen has objected to the term “far right” ever since she succeeded her father, Jean-Marie Le Pen, as the leader of the NF almost three years ago. Her threat to sue the media is a new phase in a highly successful campaign to “de-demonise” the party by expelling outright racists and abandoning the coded, and open, anti-Semitic remarks of her father.

As President François Hollande struggles for credibility and the centre-right opposition engages mostly in internal brawls, Ms Le Pen’s poll ratings have risen sharply in recent months. In a TNS-Sofres poll published by Le Figaro yesterday, 33 per cent of those questioned said they would like to see her play an important role in the years ahead.

This made her third equal with three leading centre-right politicians. As the “future face” of French politics, she was beaten only by the former President Nicolas Sarkozy (35 per cent) and the rising star of the left, the Interior Minister, Manuel Valls (43 per cent). Another recent poll, however, suggested that 70 per cent of French people would never vote for Marine Le Pen. Hence her latest move in the “de-demonisation” campaign.

Whether suing the media is good PR remains open to question, though. Her father brought similar law suits in 1995. The courts refused even to consider his political arguments which distinguished between “nationalism” and “populism”, on the one hand, and a xenophobic far or extreme right on the other. They said any attempt to “censor the vocabulary of journalism” would be an “abuse of the law”.

Since taking charge, Ms Le Pen has moved the party to the left on social questions such as divorce, abortion and gay rights, and she did not campaign against gay marriage. Her new focus – anti-immigrant, anti-Brussels, anti-Islam – has drawn fresh support. But critics insist that the party’s DNA remains largely that of the neo-fascists, anti-Semites, anti-government populists and Vichy sympathisers who founded the party in 1972.