Mr Mitchell is said to be seeking redress for what he believes has been a “campaign of vilification” against him by the paper.
A file of evidence linked to the investigation into “Plebgate” has been passed to prosecutors, Scotland Yard said last night.
So far, three officers have been arrested as part of the investigation sparked by the row which led Mr Mitchell to quit his Cabinet post.
Those arrested include a 52-year-old from the Diplomatic Protection Group who was held on 15 December on suspicion of misconduct in public office and bailed until April. Two 46-year-olds from the same command were held on 31 January and 1 February for allegedly passing information to the media and bailed until May. All three remain suspended.
A 23-year-old man who does not work for the police was also arrested and bailed until May.
The row ignited when Mr Mitchell was accused of a rant against officers as he left Downing Street on 19 September.
Pressure intensified after the Daily Telegraph published a police log of the incident, which claimed he called officers “plebs” and swore at them repeatedly.
He insisted he did not use the words attributed to him, and later said he was the victim of a deliberate attempt to “toxify” the Tories and ruin his career. An e-mail from a civilian witness backing up the police account of events has also since been called into question.
Detectives have taken statements from all 800 DPG officers.