The Metropolitan Police Commissioner has said he has an "open mind" regarding the conduct of officers in the Andrew Mitchell "plebgate" row.
Sir Bernard Hogan-Howe said it had "yet to be proven" whether a police log of an argument between the ex-chief whip and officers outside Number 10 was true.
If officers were found to have lied or made up evidence, it would be "very serious", he told MPs at a Home Affairs Committee hearing on 8 January 2013.
Mr Mitchell resigned over the row but denies calling officers "plebs".
A constable who was not on duty at the time, was arrested last month on suspicion of misconduct in a public office. The officer's claim, made to his local MP, that he independently witnessed the row is being investigated.
Appearing before the Home Affairs Select Committee, Sir Bernard said he was "sorry" if comments he made last year had given the impression he had a fixed view about the incident.
Earlier in the session, MPs took evidence on leadership and standards in the police service, and on localised child grooming.
Sir Hugh Orde and Deputy Chief Constable Simon Edens from the Association of Chief Police Officers were questioned on integrity in the police service and how to combat anti-social behaviour.
In a separate part of the session, the committee took evidence on child grooming from Martin Kimber, the chief executive of Rotherham Metropolitan Borough Council, and Joyce Thacker, the council's director of children's services.
In May 2012, nine Asian men were imprisoned for grooming and sexually exploiting white girls in their early teens in Rochdale, Greater Manchester.