AFP warned former federal government MP George Christensen was blackmail risk due to South-East Asia 'activities'

The former Coalition government was warned by federal police former Nationals MP George Christensen was at risk of being blackmailed because of "activities" he engaged in in South-East Asia.

The detail is contained in a 2018 letter from the Australian Federal Police (AFP) to then-Home Affairs Minister Peter Dutton, which police and Christensen fought on numerous occasions since 2019 to keep secret.

In the letter written by former Deputy Commissioner Ramzi Jabbour, police said a probe into the former Nationals MP's frequent travel to the area did not find evidence of "criminal conduct" but did warn he had "engaged in activities that could potentially place him at risk of being targeted for compromise by foreign interests".

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It revealed the police assessment started following a tip-off in September 2017, after a "source previously unknown to the AFP" alleged Christensen "engages in improper conduct overseas potentially in contravention of Australian law".

9News has been fighting since July 2019 for this letter to be made public under Freedom of Information laws.

Australian Federal Police argued it shouldn't be released on the grounds of privacy, then later argued it could damage national security.

Christensen has always claimed coverage and questioning of his frequent travel to South-East Asia was a vile smear.

He made three secret submissions to the information watchdog in his fight to prevent the letter from being released.

Christensen spent 294 days in the Philippines over four years from 2014-2018, leading to him being dubbed the "Member for Manila" by some of his colleagues.

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Last October, the former MP denied trying to block the release of the letter, but said he objected to it being public.

"I'm not happy with, basically documents that falsely accuse me of a serious crime being made public because therefore people will get to then report what you are falsely accused of and that's just wrong for anyone," he told 9News.

Dutton was among a number of high-profile government figures to be briefed by the AFP on its assessment of Christensen's travel.

Former Prime Minister Malcolm Turnbull was briefed six times while he was in the job, and former Nationals leaders Barnaby Joyce and Michael McCormack also received police briefings.

The Information Commissioner ruled in favour of 9News, handing down its finding on the letter on June 30. It was only released after an appeal deadline lapsed.

In her report, Commissioner Angeline Falk said she was "persuaded that a public purpose would be served through the release of the document by increasing scrutiny, discussion, comment and review of government's activities".

Christensen did not respond to requests for comment on Tuesday.