I unwittingly revealed a French political scandal, but the Fillons' downfall gives me no pleasure

In January 2017, François Fillon was well on the way to becoming the next president of France.

Had he succeeded, with a manifesto that appealed to the full spectrum of rightwing voters – cuts to benefits, increases to working hours, upping the pension age and slashing 500,000 public service jobs – the coronavirus would have hit a very different France.

Instead Fillon, who claimed to be above all suspicion of wrongdoing, was accused of having his supposedly squeaky-clean hands in the public purse. Emmanuel Macron won the election and the rest, as they say, is history.

On Monday, Fillon and his Welsh-born wife Penelope were convicted of embezzling around €1m of taxpayers’ money for nonexistent jobs.

The smoking gun that played a part in the investigation was a 2007 interview I did with Fillon’s wife. In it, unbeknown to either of us at the time, one answer would emerge a decade later and send the couple not into the presidential palace but a criminal court.

Being unwittingly involved in a political scandal in my adopted country has been a deeply unnerving experience. Journalists covering news should not be the story and rarely are, thankfully.

Scandal was the furthest thing in mind when I first approached Penelope Fillon for an interview in 2007. Her husband had been appointed prime minister, she is Welsh; it was hardly Watergate or Profumo but still, a good “soft” scoop for a British newspaper.

On Friday 18 May, I was in Normandy for the weekend when Fillon’s office called. Penelope had agreed to the interview: I was to be at a cafe in Paris’s chic 6th arrondissement the following day at 9am sharp. I scrambled to catch the 4am milk train back to Paris, and a photographer was diverted from another assignment in Europe with orders to take pictures and video the meeting.

Penelope Fillon, as noted in the article, came across as no nonsense and self-effacing. She seemed uncomfortable to be in the limelight, and said she preferred the family home in the countryside to Paris soirées.

At the time it was rumoured that Cécilia Sarkozy, the then wife of Nicolas Sarkozy, was the power behind the president. Did Penelope Fillon play the same role for the prime minister, I asked. She said: “I have never actually been his assistant or anything like that. I don’t deal with his communication.” The comment did not even make the final edit of the published article. I thought no more about it.

Fast forward 10 years to January 2017, and Fillon has graduated to the role of France’s first lady in waiting. Again, I approached her for an interview; again she agreed.

Related: François Fillon found guilty of embezzling public funds

Before we had a chance to organise a date, the investigative satirical newspaper, Le Canard enchaîné, accused Fillon of paying his wife and children for nonexistent jobs. The report quoted my article and suggested that she could not be working for her husband as she had told me she was studying for an English literature degree at the Open University (Le Canard was evidently unaware that the OU is a distance-learning institution).

I emailed her, saying I regretted that some elements of our 2007 interview had been taken out of context, namely the OU misunderstanding, and waited to be given a date for our second interview.

I had no thought of the fateful 2007 comment, sitting like a time bomb in my notebook, until the France TV’s investigative programme, Envoyé spécial, traced the photographer who was present in 2007 and obtained his video. At that point, I unearthed the 10 year-old notebook in which – in clear, readable Pitman shorthand – was the quote saying she had never been her husband’s assistant.

Fillon’s response to the Envoyé spécial exposé was to shoot the messenger. As they flailed to save the presidency, he and his campaign team took to television and social media to accuse me publicly of dissembling. He published my private emails to his wife, suggesting I was apologising for the scandal. I wasn’t. The inevitable pile-on happened.

“Just who is Kim Willsher?” asked French publications, trawling through my website and articles for clues.

On holiday in a communications black hole in Suffolk, I stood in the bitter cold outside a supermarket, the only place I could get a phone signal, trying to refute the slurs against my professionalism.

I referred everyone to the video, telling them: watch it. Penelope Fillon said what she said.

In the past three years I have refused all interview requests. I was not questioned by the police or asked to give evidence during the trial, which I did not attend. In court, Fillon argued the word “assistant” as used by his wife in our interview meant something different in English!

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In 2007, I had a certain sympathy for Penelope Fillon. I remembered her saying she was studying for another degree – she already had one in French – because her five children viewed her as “just a mother”. She wanted to show them she was “not that stupid”.

Again, in 2017, I felt a certain sympathy that our previous encounter had come back to savage her and emailed her to that effect. She passed the email to her husband, who published it to try to discredit me. But François Fillon’s dismissive behaviour to her in the wake of the scandal did him no honour. At rallies she often appeared crushed and close to tears.

People have asked if I feel vindicated. I take no personal pleasure in the Fillons’ downfall. I had no political agenda when I interviewed Penelope Fillon in 2007, nor the slightest idea that the subsequent article would throw some light into a dark corner of French politics 10 years later. But I am pleased it has. I still keep all my notebooks and I still have good shorthand, only these days I make sure I record even “soft” interviews.

• Kim Willsher is an award-winning foreign correspondent based in Paris