Federal investigators exploring the start of the Russia probe grilled the author of a controversial “dossier” that alleged election meddling and possible collusion with President Trump’s campaign — and learned enough to extend the investigation.

Three lawyers from the Justice Department’s Inspector General’s office had a sitdown in early June with author Christopher Steele in Britain, Reuters reported Tuesday.

The interview with Steele — a former top spy on Russia for Britain’s Secret Intelligence Service, or MI6 — took place while Trump was in London for a state visit with Queen Elizabeth and a meeting with Prime Minister Theresa May.

Steele’s dossier, made public in 2017, alleged that Moscow attempted to interfere in the 2016 presidential election and that there was potential collusion with Team Trump, along with other unverified and salacious claims about the president.

The Justice Department’s inspector general has been examining the earliest stages of an FBI investigation of Trump, Hillary Clinton, Russia and former Trump adviser Carter Page.

Inspector General Michael Horowitz launched his probe in March 2018 amid allegations by Republican lawmakers that the FBI erred in seeking a warrant to monitor Page.

Trump has described the Steele dossier as “bogus” and Republicans have long sought to discredit the FBI’s investigation, which was later taken over by special counsel Robert Mueller.

His final report on Russia and the Trump campaign was released in redacted form in mid-April.

In that same month, Attorney General William Barr, who now heads the Justice Department, told a congressional committee that the Horowitz probe would be completed by May or June.

One of the two sources told the wire service that Horowitz’s investigators appear to have found Steele’s information sufficiently credible to have to extend the investigation. Its completion date is now unclear.

A key focus of the Horowitz probe is whether the FBI followed proper procedures when it applied for a warrant with the Foreign Intelligence Surveillance Court to secretly conduct surveillance on Page and his ties to Russia.

Declassified documents show that the FBI cited information in Steele’s dossier when it asked the secretive FISA court in late 2016 for a warrant to eavesdrop electronically on Page, an American businessman with interests in Russia.

Mueller’s report, released on April 18, said that Russia did meddle in the election in an attempt to boost Trump’s candidacy.

It said Trump campaign officials had multiple contacts with Russian officials, but found insufficient evidence to establish a criminal conspiracy between the campaign and Moscow.

The report also described numerous attempts by Trump to impede Mueller’s inquiry, but it stopped short of declaring that he committed a crime.

Mueller during his inquiry brought charges against 34 people, including Russian agents and ex-Trump aides.

With Reuters