Metropolitan Police Federation chairman John Tully told ITV News that Chief Whip Andrew Mitchell was "lucky not to have been arrested" on Wednesday night:
"The information I have is that Mr Mitchell did use offensive language - he used the words 'pleb' and 'morons' as well as expletives, which is totally unacceptable," he said.
"It constitutes a criminal offence under the Public Order Act, Section 5, and I would say he's very lucky not to have been arrested."
"I believe he should resign. If he chooses not to, then I believe the Prime Minister should sack him," added Mr Tully.