An internal review has found a confidential allegation of sexual misconduct against Barnaby Joyce was compromised by political interference, leading to the complainant's identity being exposed and denying the former deputy prime minister a fair hearing.

The secret review by WA Nationals state president James Hayward questioned the conduct of state MPs who had "regular" communication with Catherine Marriott, the woman who lodged a complaint with the Nationals about Mr Joyce's behaviour outside a beef industry event at Canberra's Kurrajong Hotel in 2016.

The WA Nationals instigated an investigation into the sexual misconduct allegations, which are denied by Mr Joyce. The existence of the investigation and Ms Marriott's identity were soon exposed in media reports.

According to a review of the investigation's handling, extensive contact between Nationals MPs and Ms Marriott, a former West Australian Rural Woman of the Year, may have extended to "proof reading" her formal complaint - potentially making MPs look like "co-conspirators" in a push to bring down the federal leader.

The sexual harassment allegations had been the subject of rumour for some time and the decision by WA Nationals to formalise the matter in February led to a belief by some Nationals that the complaint was "weaponised" to bring an end to weeks of damaging headlines over Mr Joyce's affair with former staff member Vikki Campion.