Former French president Nicolas Sarkozy described the prison where he spent 20 days as a noisy, harsh “all-grey” world of “inhuman violence" in a book released Wednesday that also offered political advice about how his conservative party should appeal to far-right voters.

In “Diary of a Prisoner,” the 70-year-old says his own tough-on-crime stance has taken on a new perspective as he recounts the uncommon turn in his life after being found guilty of criminal association in financing his winning 2007 campaign with funds from Libya.

Hundreds of supporters queued up Wednesday at a bookshop in a Paris upscale residential neighborhood where Sarkozy staged his first book signing.

Read moreEx-president Sarkozy’s 20-day prison diary: ‘Like the Count of Monte Cristo’?

The court sentenced him in September to five years in prison, a ruling he appealed. He was granted release under judicial supervision after 20 days behind bars.

The book provides a rare look inside Paris’ La Santé prison, where Sarkozy was held in solitary confinement and kept strictly away from other inmates for security reasons. His loneliness was broken only by regular visits from his wife, supermodel-turned-singer Carla Bruni-Sarkozy, and his lawyers.

Sarkozy wrote that his cell looked like a “cheap hotel, except for the armored door and the bars,” with a hard mattress, a plastic-like pillow and a shower that produced only a thin stream of water. He described the “deafening noise” of the prison, much of it at night.

Opening the window on his first day behind bars, he heard an inmate who “was relentlessly striking the bars of his cell with a metal object.”

“The atmosphere was threatening. Welcome to hell!”

Sarkozy said he declined the meals served in small plastic trays along with a “mushy, soggy baguette” – their smell, he wrote, made him nauseous. Instead, he ate dairy products and cereal bars. He was allowed one hour a day in a small gym room, where he mostly used a basic treadmill.

Sarkozy says he was informed of several violent incidents that took place during his time behind bars, which he called “a nightmare.”

“The most inhumane violence was the daily reality of this place,” he wrote, raising questions about the prison system’s ability to reintegrate people once their sentences are served.

Sarkozy, known for his tough rhetoric on punishing criminals, said he promised himself that “upon my release, my comments would be more elaborate and nuanced than what I had previously expressed on all these topics.”

Le Pen’s party ‘not a danger for the Republic’

Beyond recounting prison life, Sarkozy used the book to offer strategic political advice for his conservative Republicans party and revealed he spoke by phone from prison with far-right leader Marine Le Pen, once a fierce rival.

Le Pen’s National Rally is “not a danger for the Republic,” he wrote. “We do not share the same ideas when it comes to economic policy, we do not share the same history … and I note that there may still be some problematic figures among them. But they represent so many French people, respect the results of the elections and participate in the functioning of our democracy.”

Sarkozy argued that the reconstruction of his weakened Republicans party “can only be achieved through the broadest possible spirit of unity.”

Sarkozy’s new book revives controversy in French right

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The Republicans party has in recent years been moving away from a position held among parties for decades that any electoral strategy must be aimed at containing the far right, even if it means losing a district to another competitor.

Still, political analyst Roland Cayrol said Sarkozy’s comments came like “a thunderclap” in the decades-long position of French conservatives that the National Rally doesn’t "share the same values” and “no electoral alliance is possible” with the far right.

The former president from 2007 to 2012 has been retired from active politics for years but remains very influential, especially in conservative circles.

In the wake of Sarkozy’s comments, the Republicans’ top officials have stopped short of calling for any actual cooperation deal with the National Rally, but instead indicated they want to focus on ways to get far-right voters to choose conservative candidates.

Sarkozy also mentioned his former friendship with centrist President Emmanuel Macron. The two men met at the Élysée presidential palace just days before Sarkozy entered prison.

According to Sarkozy, Macron raised security concerns at La Santé prison and offered to transfer him to another facility, which he declined. Instead, two police officers were assigned to the neighboring cell to protect him around the clock.

Sarkozy said he lost trust in Macron after the president did not intervene to prevent him from being stripped of the Legion of Honor, France’s highest distinction, in June.

Last month, Sarkozy was convicted of illegal campaign financing of his 2012 reelection bid, in a major blow to his legacy and reputation. He was sentenced to a year in prison, half of it suspended, which he now will be able to serve at home, monitored with an electronic bracelet or other requirements to be set by a judge.

Last year, France’s top court upheld an appeals court decision that had found Sarkozy guilty of trying to bribe a magistrate in exchange for information about legal proceedings in which he was involved.

*(FRANCE 24 with AP) *