Outgoing Australian Greens senator Bob Brown says his biggest political blunder almost saw him ban lesbian sex in Tasmania.

Senator Brown told the National Press Club today that during a tactical 1986 attempt to get a ban on male homosexuality in Tasmania overturned, he accidentally made lesbian activity illegal.

Bob Brown Credit:Alex Ellinghausen

He said that he was saved from his terrible mistake by then Queensland Premier Joh Bjelke-Petersen, had declared he wouldn't countenance banning lesbian sex.

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Senator Brown whose resignation comes into effect in 10 days, says once Bjelke-Petersen's stance became known to Tasmania's upper house they voted down the amendment and saved his skin.

AAP