James Comey used his personal Gmail account to conduct FBI business on numerous occasions when he was director - even though he was investigating Hillary Clinton for using a private email server and had warned FBI staff they would be in 'huge trouble' for doing the same thing, a scathing watchdog report revealed on Thursday.

The report from Justice Department inspector general Michael Horowitz found 'numerous instances' where Comey used his Gmail account to conduct the bureau's business, which was 'inconsistent' with Justice Department policy.

Ironically, the report noted when Comey spoke at an FBI conference in October 2016, he warned employees they would be in 'huge trouble' if they used a private email service as Clinton did.

James Comey used his personal Gmail account to conduct FBI business on numerous occasions

He was investigating Hillary Clinton for the same thing

Comey, when he spoke at the FBI's annual SAC Conference in San Diego, said: 'I have gotten emails from some employees about this, who said, 'If I did what Hillary Clinton did I'd be in huge trouble.' '

'My response is you bet your ass you'd be in huge trouble,' Comey said in that speech.

'If you used a personal email, Gmail or if you [had] the capabilities to set up your own email domain, if you used an unclassified personal email system to do our business in the course of doing our business even though you were communicating with people with clearances and doing work you discussed classified matters in that, in those communications, TS/SCI, special access programs, you would be in huge trouble in the FBI,' Comey said.

'Of that I am highly confident,' he added. 'I'm also highly confident, in fact, certain you would not be criminally prosecuted for that conduct.'

Nick Merrill, who was Clinton's spokes person on the 2016 campaign, retweeted a reporter's tweet about Comey's Gmail use with the words: 'I'll just leave this here.'

Comey was criticized in IG report for usurping the power of the attorney general in his handling of the investigation into Clinton's use of a private email server for State Department business.

The then FBI director said in July 2016 that he was not recommending any criminal charges in Clinton's case.

But he caused a huge kerfuffle when, days before the election, he announced he would revisit the probe after the discovery of new emails, a move that the Clinton camp has blamed for her loss.

None of the emails Comey sent to his Gmail account contained classified information, according to IG report.

Comey defended his use of his Gmail to investigators, saying he only used it for public speeches and statements.

I used it 'when I needed to word process an unclassified [document] that was going to be disseminated broadly, [such as a] public speech or public email to the whole organization,' he told them.

The former FBI director also said his use of his Gmail was 'incidental' and because he made sure the work got forwarded to a government account so 'I wasn't worried from a record-keeping perspective.'

He added: 'I wasn't doing classified work there, so I wasn't concerned about that.'

He explained to investigators 'I did not have an unclass[ified] FBI connection at home that worked.'

The IG report found five instances when Comey forwarded an unclassified FBI email to his personal Gmail account.

Those included one on November 8, 2016, that proposed a post-election message for all FBI employees that was entitled 'Midyear thoughts.'

The report from Justice Department inspector general Michael Horowitz found five instances where Comey used his personal Gmail

Hillary Clinton's campaign spokesman tweeted his response to the news

In late December 2016, Comey forwarded multiple drafts of a proposed year-end message to FBI employees.

On December 30, 2016, Comey forwarded proposed responses to two requests for information from the Office of Special Counsel.

On January 6, 2017, Comey forwarded an email from Chief of Staff Jim Rybicki highlighting language that needed to be corrected in a Wall Street Journal article.

In mid-March 2017, Comey sent from his personal email account to his own and Rybicki's unclassified FBI accounts multiple drafts of Comey's proposed opening statement for his March 20, 2017 testimony to the House Intelligence Committee.

Investigators asked Comey if the use of his personal email was in accordance with FBI regulations.

'I don't know,' he said. 'I think so, but I don't know. I remember talking to Jim [Rybicki] about it at one time, and I had the sense that it was okay.'

Rybicki was also asked by investigators to explain the email use.

He responded to them via email: 'In rare circumstances during his tenure, Director Comey sends unclassified emails from his official FBI.gov email account address to [his Gmail account]. This permits him to open attachments and use his personal laptop to then work on a speech or other content intended for wide dissemination. He then sends drafts or the completed text to his official FBI.gov email account or to another FBI.gov email account from [his Gmail account]. He opened this personal account at about the time he became Director.... To ensure a high level of cybersecurity, Director Comey routinely deletes all emails from his [Gmail] account each day, and then clears the deleted messages folder. He began this practice about two years ago. The Director does not recall receiving and/or seeking advice concerning the use of these accounts.'

Comey offered his response to the IG report in an op-ed he wrote for the New York Times, which did not include any mention of his use of his Gmail account.

'The inspector general's team went through the F.B.I.'s work with a microscope and found no evidence that bias or improper motivation affected the investigation, which I know was done competently, honestly and independently,' he wrote.

'The inspector general's office has now reached that very conclusion. Its detailed report should serve to both protect and build the reservoir of trust and credibility necessary for the Department of Justice and the F.B.I. to remain strong and independent and to continue their good work for our country.'