Relations between Mr Jean-Marie Le Pen, the NF President, and the party's de facto second power, Bruno Megret, have become so poisonous that some insiders are predicting a permanent split in the movement in the next few weeks.
At the same time, the NF is about to announce a considerable public relations coup. Charles de Gaulle, the late President's grandson who is an obscure right-wing Euro MP, is expected to join the NF list in the European elections next year, although not the party.
Even this is likely to fuel the internal feuding within the NF. Two of the party's most powerful clans are Vichy apologists and former Algerian colonists, both of whom regard the original De Gaulle as a traitor to France.
Other party insiders suggest that the Le Pen-Megret quarrel over who should lead the NF list at the Euro-elections can still be patched up if both men are prepared to compromise. But the long-suppressed struggle for the succession to Mr Le Pen seems to be spinning out of control.
To the amusement of outsiders, the battle is being fought with the unscrupulous vituperation. "Le Pen is ready to break his toy rather than let go of it," said one Megret supporter.
Another senior NF official told Le Monde that the 70-year-old Le Pen was going through "a crisis of senility".
A leading Le Pen backer described the group of clever, careerist young men surrounding Mr Megret, 49, as politicians who expected to go straight from "baby food" to the cabinet.
A meeting of the NF political bureau on Monday - at which Mr Le Pen threatened to throw two of Mr Megret's lieutenants out of the party - produced screaming and shouting so loud that it could be heard in neighbouring rooms in the party's headquarters in Saint Cloud, south-west of Paris.
Mr Megret is outwardly a more moderate and practical man than Mr Le Pen, but is said to be privately even more extreme in his racial and nationalist views. Although detested by many in the NF, he has stealthily built his own power-base.
Mr Megret also knows more about the internal dealings of the NF - and especially its mysterious finances and the personal finances of Mr Le Pen - than any other man but "Le Chef" himself. If he is forced out, as seems possible, he will try to bring down the temple behind him. "Le Pen's courtesans dream of a purge ... but Megret is not an isolated figure. His expulsion would blow the movement apart," one Megret supporter told Liberation.
Behind the struggle is the belief of the Megret supporters that the "old man" is holding back the NF. He is seen - not without reason - as a wrecker and rabble-rouser, with no real interest in power. Mr Megret believes that the NF could move on, post-Le Pen, to be the pivotal force in a French political scene shifted sharply, and permanently, to the right.
The immediate cause of the quarrel is the judgment banning Mr Le Pen from seeking political office for two years. The ban was part of his punishment for a physical assault on a female Socialist candidate during the parliamentary election campaign last year.
If Mr Le Pen's appeal is turned down by a court in Versailles next month, he will be unable to head the NF list in the Euro-elections in June. In that case, Mr Megret expects to lead the NF list, which would make him a clear candidate for an early succession to the party's leadership.
Not at all, retorted Mr Le Pen. If he lost the appeal, the leader of the NF list would be his own wife, Jany (someone with no previous experience of politics).
This was supposed to be a political master-stroke to which Mr Megret could not object. But Catherine Megret ran successfully for mayor of Vitrolles, near Marseilles, last year when her husband was banned for electoral irregularities.
In the event, Mr Megret's supporters used the decision to tar Mr Le Pen within the NF as a nepotist and autocrat, driven by personal vanity and not the nationalist cause.
Mr Megret forced the decision to be formally withdrawn. Undeterred, Mr Le Pen has moved in recent weeks to purge Megret and his supporters from the Euro campaign team.
In an unusually blunt interview this week with the NF-leaning newspaper, Present, Mr Megret declared: "No one is the proprietor of the National Front. Our movement belongs to its supporters and electors, to the French, to France."