The embodiment of the political establishment is suddenly favourite to face Marine Le Pen in next year’s election

In an exhibition hangar near Lyon airport as thousands of supporters waved French flags, a well-heeled country gentleman seen as the figurehead of the traditional Catholic provincial French right, took to the stage with a contented smile.

François Fillon, the former prime minister who in a 35-year political career has come to embody the very essence of the French political establishment, shouted to the well-dressed, largely elderly crowd: “We have to change the system!”

Fillon is the dark horse who is suddenly favourite to win the right’s nomination for presidential candidate on Sunday, and thus likely to face the far-right Front National’s Marine Le Pen in the race to lead France next year.

An amateur racing driver and unrepentant Margaret Thatcher fan who has broken ranks with the traditionally statist line of the French right, he has promised a “radical shock” for France – tax cuts, public spending cuts, slashing public sector jobs and breaking trade union power.

His popularity is also down to his careful appeal to the deeply socially conservative views of the Catholic right, promising to reverse certain recently won adoption rights for gay couples, preserve traditional family values and respect France’s Christian roots.

“France is more rightwing than it has ever been,” Fillon said this week, positioning himself as the only candidate who could fully tap into that mood.

If Fillon’s promises of radical economic reform and “freedom from French bureaucracy” sound familiar, it is because they are. His shock-therapy plans are an echo of what the rightwing Nicolas Sarkozy promised when he swept to power in 2007, but failed to deliver.

Facebook Twitter Pinterest Fillon and Nicolas Sarkozy in 2010, when they were prime minister and president. Photograph: Charles Platiau/Reuters

Fillon was Sarkozy’s prime minister for five years, and would normally bear part of the blame for the failures of the Sarkozy era. But he has broken free of the stigma that haunted the former president and – styled as “Mr Austerity” – now promises to go further than any French leader has dared before, raising the retirement age, transforming labour laws and praising Thatcher’s Britain as a model success story.

It is, however, Fillon’s social conservatism and “family values” – including his private views on abortion and his drive to limit adoption rights for same-sex couples – that have become a focus of the bitter second round run-off to win the right’s presidential nomination.

His more moderate centrist opponent, Alain Juppé, has accused Fillon of wanting to drag France back into the past, with “an extremely traditionalist vision, not to say slightly retrograde vision, of the role of women, the family and marriage”. He insisted Fillon must clarify his position on abortion.

Fillon, who abstained when parliament was voting on a 2014 law on the equality of men and women, has previously said that as a Catholic he is personally opposed to abortion but would not try to change the 1975 law that legalised it in France. Furious that the abortion issue was being dragged into the debate, he said it was “grotesque and ridiculous” that he was being “billed as a medieval reactionary”.

Born in a traditionally Catholic region of western France, Fillon, 62, who with his Welsh wife raised his five children in a 12th-century chateau, has the support of hardline groups that oppose France’s same-sex marriage law. When the Socialist government introduced the legislation three years ago, it led to huge street protests, and the fractures in French society have not healed.

Facebook Twitter Pinterest Fillon with his Welsh wife, Penelope. Photograph: Xavier Laine/Getty Images

At his rally in Lyon on Tuesday night, leading figures from those street protests were present to applaud him. “I will put the family at the heart of all public politics,” Fillon promised to cheers. The family was “certainly not a place for dangerous social experimentation”, he said – by which he meant new adoption rights for same-sex couples.

In 2013, Fillon voted against the introduction of same-sex marriage, and as a young MP in 1982 he voted against the law that in effect legalised homosexuality by setting an equal age of consent.

The centre-right gay rights association GayLib described his vision of France as “clearly hostile to LGBT people”.

When it emerged this week that while prime minister, Fillon had told the junior minister Nathalie Kosciusko-Morizet that she would not be promoted to a full ministerial job “because you’re pregnant”, Fillon shrugged it off, saying his comment had been clumsy and a bad joke, and that he had apologised to her at the time.

Fillon has vowed to defend France’s history and Christian roots. The crowd in Lyon cheered his promise to bring back school uniform and rewrite the history curriculum to tell the “national story” of France and get rid of an analytical focus on questioning history, which he said was about “doubting” France.

Facebook Twitter Pinterest Fillon addresses the rally in Lyon on Tuesday. Photograph: Guillaume Horcajuelo/EPA

Several figures from the right of the party were in the audience, including the former minister Nadine Morano, who was banned by Fillon’s Les Républicains party from running in last year’s regional elections after she repeatedly insisted France was a “white race” country.

Fillon’s sudden rise in popularity is in large part due to a book he published this autumn called Conquering Islamic Totalitarianism, which won him support on the right.

In it, he lambasted the current French government for failing to deal with the Islamic terrorism that had seen more than 230 people killed in France in a period of 18 months. Leaning towards the “clash of civilisations” theory developed in the 1990s by Samuel Huntington, Fillon warned that “the bloody invasion of Islamism into our daily life could herald a third world war”.

In Lyon, he was loudly cheered when he said: “Radical Islam is corrupting some of our Muslim fellow citizens.” He promised administrative controls on Islam in France, including dissolving the Salafi movement and banning preaching in Arabic. This summer he supported a law to ban burkini full-body swimsuits from French beaches.

Foreign policy is also a point of friction between Fillon and Juppé – namely Fillon’s call to mend ties with Russia and work with the Syrian regime of Bashar al-Assad. Fillon, who is on first-name terms with Vladimir Putin after they were prime ministers during the same period, is against the European sanctions against Moscow over the conflict in eastern Ukraine.

He said this week that France’s war against “Islamic totalitarianism” meant “we’ll need lots of allies, among them Russia”. He brushed off Juppé’s attacks that he should “go easy on the vodka”. He said the fight against Islamic State meant France should not rule out cooperating with Assad. On Wednesday Putin told reporters in Moscow Fillon was an “upstanding person.”

One key question for next May’s presidential election is whether Fillon could serve as a bulwark against Le Pen, who all polls currently show will make it to the final round run-off. He is ferociously opposed to the far-right. His focus on traditional French family values and identity appeals to a part of her conservative voters and, at his Lyon rally, he used elements of Le Pen’s vocabulary, stressing the “sovereignty” of France and regularly talking of “the people”.

Unlike Sarkozy and Juppé, he has no historic corruption conviction or legal inquiries against him, so it is harder for Le Pen to attack his integrity. She will, however, attack him mercilessly as a face of the past, a symbol of the system and Sarkozy’s prime minister. Her economic platform, which is protectionist, statist and more economically leftwing, is diametrically opposed to his. Fillon said his reforms would stem extremism in France: “To stop extremists, you need results, real and quick change.”

Facebook Twitter Pinterest Fillon’s supporters wave flags at the Lyon rally. Photograph: Jean-Philippe Ksiazek/AFP/Getty Images

In the crowd, Roger Auguste, 69, a retired electronics worker from a small village south of Lyon, said he was going to vote for Fillon in the final round of the right’s primary after backing Sarkozy, who had been eliminated. “He’s discreet, capable, experienced. He represents a part of France that’s rightwing, free-market, traditionalist and for the family,” he said.

A 26-year-old junior doctor working in the casualty department of a big Lyon hospital said that although she disagreed with his drive to cut 500,000 public sector jobs in five years – “hospitals are already struggling to function on the staff levels we have” – she felt Fillon was the only person who could fix the French economy and security. “We have had so many terrorist attacks. We can’t continue like this,” she said.

“I like him because he knows what he wants,” said Aline Duret, 70, a retired teacher. “He wants to cut immigration. We have to find a solution to stop migrants coming in.”