Former government minister Andrew Mitchell is being sued for libel by a police officer he accused of lying during the Plebgate saga.
PC Toby Rowland is suing Mitchell for defamation over a press conference, during which the former chief whip said the officer lied in stating Mitchell used the word "pleb."
Mitchell issued the claim last month following the publication of a report in to the long-running episode last year, which cost him his government front-bench job.
No charges were brought against Rowland by the Crown Prosecution Service because there was "insufficient evidence" he lied in his account of the incident. Mitchell continues to dispute Rowland's central claim that he said "pleb" to officers, claiming he was the victim of a "stitch up."
Rowland is being supported in the costly proceedings by the Police Federation, which has clashed with the government over policing reform. The new libel case brings to two the number of defamation proceedings active over the affair - with Mitchell suing The Sun newspaper over its reporting of the case.
A spokesman for the Federation said: "We can confirm that PC Toby Rowland yesterday issued a letter of claim for libel against Andrew Mitchell MP. This relates to comments he made following the media-termed Plebgate incident in Downing Street in 2012.
"The Federation has supported PC Rowland with the provision of legal advice in respect of this matter. All subscribed members of the Police Federation are entitled to such support for legal representation as they see fit.
"Such applications are considered carefully by the Federation and then passed on to legal representatives to consider the legitimacy of any case before a decision is made on any such legal proceedings. That has been done in this case."
Announcing its findings last month, the CPS said: "We have found that there is insufficient evidence to show that the officer at the gate lied in his account. The CPS has also found that there is insufficient evidence to show that Mr Mitchell was the victim of a conspiracy of misinformation."
No comment was available from Andrew Mitchell's office on proceedings against him at time of publication.