The police investigation into the "plebgate" affair, which led to the resignation of the former chief whip Andrew Mitchell, has cost nearly £150,000, it has emerged.
Scotland Yard launched Operation Alice after claims that officers might have lied about the dispute with Mitchell when they refused to let him leave Downing Street on his bicycle through the main gate in September. It was claimed at the time that Mitchell swore at the officers and called them plebs.
But a subsequent Channel 4 investigation cast doubt on that account when it revealed CCTV footage which showed there was not a large group of tourists outside the main gate at the time as had originally been claimed.
An email from a civilian witness backing up the police account of events has also since been called into question.
Mitchell, who strenuously denies the allegation that he called the officers plebs, resigned after a series of damaging headlines.
In a letter from the deputy assistant commissioner Patricia Gallan, who is leading the investigation, to Keith Vaz, chairman of the Commons home affairs select committee, it was disclosed that the cost of the police investigation had reached £144,000.
Gallan wrote: "It remains that I have 30 officers at my disposal and Operation Alice is estimated to have cost £144,000 to date. Four people have been arrested and no individual is currently charged. The advice file submitted to the Crown Prosecution Service by the MPS [Metropolitan police service] has specifically asked for advice and guidance surrounding the future of the investigation in relation to potential criminal charges."
Last week, a letter from Deborah Glass at the Independent Police Complaints Commission to Mitchell disclosed that the CPS was considering whether to charge anyone in relation to the incident.
Her letter revealed the extent of the investigation so far. Detectives have taken 740 statements, 44 of which have been described as key, and have interviewed seven officers and one member of the public under caution. In total, 133 exhibits and 93 documents will be reviewed by prosecutors.
Vaz said on Friday: "We look forward to seeing DAC Gallan when her investigation is completed."