Yvette Cooper, Shadow Home Secretary, said:
"It is essential that there is a full and independent investigation into what happened in Downing Street as we and others called for three months ago.
"These are very serious allegations involving a police officer must be rigorously investigated. And the full facts must be set out. None of the reports from the Government in September raised the possibility of a witness nor is it clear whether this was checked out at the time or had any influence on events.
"Andrew Mitchell admitted swearing at the police. The Met Commissioner is standing by the accounts from the police officers present at the gate, which Andrew Mitchell has now said are untrue.
“The Prime Minister was urged repeatedly to set up a proper investigation to get to the facts and refused to do so, and it is incredible that three months on we still don't have clarity about what happened.
"Given the seriousness of this issue and the importance of trust between the police and Government Ministers, this must not be allowed to drag on any longer."