By Tim Castle
LONDON (Reuters) - British police investigating claims an officer fabricated evidence that led to a minister resigning said on Wednesday they were looking for any signs of a conspiracy in an affair that could damage the force's reputation.
The officer posed as a member of the public and falsely claimed to have witnessed a row between cabinet minister Andrew Mitchell and police outside Prime Minister David Cameron's Downing Street office, according to a Channel 4 News report.
Mitchell quit as the "Chief Whip" in charge of maintaining discipline in Cameron's parliamentary Conservative party in October following weeks of negative headlines in which he failed to shake off the accusation that he called the officers "plebs".
The class-ridden insult was highly damaging for Mitchell and the Conservatives because it played into opposition claims that the government is elitist and out of touch with ordinary Britons squeezed at a time of economic austerity.
Reports of the confrontation came just days after two unarmed female police officers were shot dead in northern England, fuelling the indignation of police representatives already angry over government reductions in force budgets.
The Police Federation, which represents ordinary officers, relentlessly exploited the "plebs" row in its campaign against the cutbacks and changes in working conditions, but has denied conspiring to unseat the minister.
Mitchell, who admitted and apologized for swearing at the officers after they refused to let him ride his bicycle through the main Downing Street gates, maintains he never uttered the pejorative word which he said was used to destroy his career.
On Wednesday, Mitchell's political fortunes were reviving with colleagues calling for his return to government as doubt was cast over the police account of the incident.
Mitchell was warmly welcomed by other lawmakers as they gathered in parliament for Cameron's weekly question and answer session.
"A police officer posing as a member of the public and sending an email potentially to blacken the name of a cabinet minister is a very serious issue and does need to be seriously investigated," Cameron told the chamber's packed benches.
Channel 4 News said the officer had not been present at the incident, despite sending an email to a Conservative lawmaker claiming to have been a witness to the row.
The officer had also not disclosed in the email he was a policeman and had posed as a concerned member of the public, the program added.
The TV report, broadcast on Tuesday, also questioned the veracity of a leaked police log of the confrontation which, like the email, said other bystanders had been present outside the gates and had been "shocked" by Mitchell's language.
Previously unseen CCTV footage of the incident aired by the program showed the street was almost empty of bystanders.
London's police force said the allegation that an officer fabricated evidence was extremely serious and went "to the very heart of the public's trust in the police service".
At the weekend it arrested a police officer on suspicion of misconduct and said it was investigating his claim to have witnessed the Downing Street incident.
It said he was a member of its Diplomatic Protection Group but was not on duty at the time.
The investigation, conducted by 30 officers, would "establish if there is any evidence of a conspiracy between this officer and any other person," the force said.
"This is a large scale and complex investigation that has grown to incorporate numerous lines of inquiry. The investigation will not be short."
(Editing by Jon Hemming)