The former British intelligence officer behind the controversial Trump dossier believes his reports are "70 percent to 90 percent" accurate, according to a new book about Russia's influence in the 2016 election written by Guardian reporter Luke Harding.

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Christopher Steele also reportedly believes the contents of his report will be verified — and his work vindicated — as special counsel Robert Mueller continues to investigate possible ties between the Trump campaign and Moscow, according to a Guardian story written about the book and published on Wednesday.

“I’ve been dealing with this country for thirty years. Why would I invent this stuff?” Steele is quoted as saying in Harding's new book, "Collusion: Secret Meetings, Dirty Money, and How Russia Helped Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE Win."

According to Harding, Steele felt shocked by his findings and the information his sources gave him about the extent of the collusion, warning friends that reading his report would be a "life-changing experience.”

Harding's book also reportedly claims that Washington insiders took the explosive allegations in the dossier seriously because of Steele's trusted reputation of reporting on Kremlin matters, according to the Guardian. Steele reportedly wrote over a hundred reports on Russia and Ukraine between 2014 and 2016.

The book details Steele's career, including his time as an MI6 officer stationed in Moscow.

"Here was a pro, a well-connected Brit, who understood Russian espionage and its subterranean tricks. Steele was regarded as credible,” Harding writes, according to the Guardian story.

Some of his reports reached the desk of former Secretary of State John Kerry John Forbes KerryThe Memo: Warning signs flash for Trump on debates Divided country, divided church TV ads favored Biden 2-1 in past month MORE and other State Department officials, the book says.

Fusion GPS, an opposition research firm, contracted Steele to investigate ties between then-Republican presidential candidate Trump and the Kremlin during the 2016 election as scrutiny over their relationship mounted.

Steele and Fusion GPS became entangled in a national controversy when BuzzFeed News published the contents of the Russia dossier, which contained unverified allegations — some of which have been proven to be false.

The report comes after the House Intelligence Committee on Tuesday interviewed Glenn Simpson, the co-founder of Fusion GPS, during a closed-door meeting that lasted nearly seven hours.

An attorney for Simpson, Joshua Levy, also defended the contents of the dossier, saying “now in hindsight [it] looks quite accurate.”

Levy also denied that Simpson had any involvement writing the dossier.