In the final weeks of the French presidential election, Nicolas Sarkozy, the centre-right candidate, is counting on his errant wife to help win him power by boosting his appeal among young voters and women.

Cécilia Sarkozy, a 48-year-old communications expert, is often described as one of the candidate’s most alluring assets and exercises enormous influence over every aspect of the campaign, say aides to Sarkozy, 52.

Since a media feeding frenzy in 2005 when she left her husband for another man only to return to him a year later — she has been keeping a low profile: she chose a fashion designer’s former workshop as the Sarkozy election headquarters but so rarely does she appear there that they call her the “ghost” of the campaign.

She is no less effective in the shadows, however, and has filled key campaign posts with friends in an attempt to ensure victory for the reform-minded former interior minister who has dreamt of becoming president since childhood.

He wants to make France more competitive and last week praised the economic success of Britain, where Judith, one of Cécilia’s daughters, works in a bank.

“Look at London,” he said at a business seminar in Paris on Friday, launching into a description of how a British jobcentre works. “After three months, if you have not found a job you go and see a special adviser who says, ‘How is that possible?’ ”

Jobcentres like that were what was needed in France, Sarkozy said. In a rapidly evolving world, he added, “We are not keeping our place.” He vowed that, if elected, he would do everything possible to turn France’s discredited 35-hour week into the minimum rather than maximum working period. “We have 1% less growth than other countries because we don’t work as much,” he said.

A diminutive figure with Napoleonic ambitions, Sarkozy is said to trust nobody as much as his glamorous wife and some refer to the willowy former model, who is much taller than him, as the “control tower” guiding him onto the presidential landing strip.

He fought tooth and nail to win her back when she abandoned him with their son to live with Richard Attias, an events organiser, in New York. Valérie Domain, an author, said Cécilia complained to her of being made to feel like “a piece of furniture” in Sarkozy’s entourage.

When she left, Sarkozy began an affair with a political journalist, apparently in an attempt to make Cécilia feel jealous. There followed a public reconciliation between the two. Then came another blazing row: Cécilia told Domain that she had seen a damaging dossier on the private life of her husband.

She returned home again, however, at the end of last year, apparently determined to claim the prize of first lady that Sarkozy had so often promised her.

She went to work as an unofficial adviser, organising events with young voters and adding her voice to those who were telling Sarkozy that he must soften his image if he was to compete with Ségolãne Royal, the Socialist candidate and first woman with a real chance of becoming president, for the female vote.

The result was a speech in which Sarkozy proclaimed, “I have changed”, and spoke about women’s issues such as combating female circumcision and creating more crèches.

Cécilia went on to secure the appointment of François de la Brosse, the husband of one of her friends, as a senior adviser to Sarkozy. He runs websites promoting the candidate to a youth audience, including one called Nicolas Sarkozy Television that shows video clips of the man in action.

De la Brosse’s daughter Alexandra has a job in the campaign press office.

Cécilia, the daughter of a Russian pianist, was also responsible for the appointment of Rachida Dati, a young woman of immigrant origin, as one of Sarkozy’s two chief spokespeople. She felt that her husband needed to reach out to the immigrant suburbs, where he was accused of inflaming tensions in 2005 by referring to young troublemakers as thugs.

She was right: rioting last week at the Gare du Nord railway station, where 13 youths were arrested in battles with police after an attempt to detain a fare-dodger, played into the hands of Jean-Marie Le Pen, the far-right National Front candidate, who caused a political earthquake in the last election in 2002 by coming second.

After Tuesday night’s confrontations, Le Pen rose two points in one opinion poll, to 15%, within striking distance of three front-runners in a wide open race for the chance to succeed President Jacques Chirac.

Although Sarkozy leads in the polls, one in two voters have not yet made up their minds and Royal is snapping at his heels.

The strength of Le Pen’s “France for the French” campaign has, much to his delight, helped to push issues of “Frenchness” to the fore and Sarkozy’s proposal for a ministry of “immigration and national identity” was met by Royal’s promise to ensure that everybody learnt by heart the words of the national anthem and flew a flag from their window on Bastille Day.

In a further nod to the right, Royal, 53, last week tried to stop rumours that she and François Hollande, the Socialist party’s secretary general and father of her four children, are no longer together. The two appeared for the first time together on stage at a campaign event in which he introduced her to the public with a kiss on the cheek.

Hollande refused, nevertheless, to pose with her as a couple in Paris Match magazine, perhaps not wanting to be used as an electoral prop. Normally reluctant to delve into the private lives of politicians, the French press justified its coverage of Sarkozy’s crisis with Cécilia on the grounds that she was a crucial part of his electoral campaign.

Since returning to her husband, Cécilia has eschewed the limelight, refusing to appear at his side despite polls showing that among all the presidential contenders and spouses they are the most popular couple, followed by François Bayrou, 55, the centrist candidate, and Babette, his wife of 36 years.

“Cécilia feels she got burnt by too much media exposure before,” said a source in the Sarkozy campaign. “For the time being, at least, she is staying out of the picture.”

That may be understandable. The couple’s marital discord became such a popular soap opera that two books were written about it, disguised as “novels”.

In one of them, Le Roman Vrai du Prétendant (The True Story of the Pretender), a figure called François Vittori — he is identical to Sarkozy in everything but name — wins the election but Marietta, the fictional shadow of Cécilia, divorces him the next morning in revenge for his philandering.

Sarkozy can only hope that reality is kinder.

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