France's main centre-right UMP party on Sunday won a by-election that had been seen as a test of a recent revival in the fortunes of the far-right Front National (FN), officials said.
The UMP's Jean-Louis Costes took just under 54 percent of the vote in a run-off against the FN candidate Etienne Bousquet-Cassagne in a contest which followed the resignation of the country's budget minister in a scandal that has severely dented the standing of the Socialist government.
Jerome Cahuzac was forced to stand down as a minister and as deputy for Villeneuve-sur-Lot in southwestern France after being exposed for having a secret overseas bank account and having repeatedly denied it existed.
Cahuzac's personal humiliation was particularly damaging for his party and politicians in general as he had been the minister in charge of cracking down on tax dodging at a time when middle earners are being asked to pay more to the state to help France put its public finances in order.
The Socialist vote in last weekend's first round of the by-election collapsed to 23.5 percent, down from a share of just over 61 percent when Cahuzac stood in the 2012 general election.
The defeated Socialist candidate had called on left-wing voters to turn out to vote for the UMP in order to prevent the FN, which won 6.4 million votes in the first round of last year's presidential election, securing a third seat in the National Assembly.
The call appeared to have been followed sufficiently to give the centre-right a comfortable margin of victory, and former Prime Minister Francois Fillon, one of the UMP's leaders, said the victory would be welcomed by "all republicans".
But Fillon also acknowledged the recent advances made by the FN on the back of the Cahuzac scandal and France's economic problems were of concern for all mainstream parties.
"The elevated score of the Front National is a reflection of the despair felt by many French who have been let down by the false promises of the president of the republic," Fillon said. "It is also a warning for the opposition."
Political analysts say the FN has benefited from efforts to "detoxify" its image under the leadership of Marine Le Pen, who is seen as a less controversial and divisive figure than her father and predecessor Jean-Marie Le Pen.