Police Federation's Ken Mackaill on Andrew Mitchell
12 October 2012 Last updated at 13:20 BST
A Police Federation rep about to meet the Conservative Chief Whip said it was time to find out who was telling the truth over the alleged "pleb" comments at a Downing Street security gate.
Ken Mackaill said it was "not a political campaign of any sort" but about the "integrity of police officers".
He said Mr Mitchell had to explain what he said or resign, adding: "Somebody is not telling the truth".
Andrew Mitchell is meeting officers on Friday afternoon after the row over what was said to an officer.