Detective texted tycoon's daughter during her trial

A Scotland Yard detective is under investigation for allegedly sending "inappropriate" text messages to the daughter of a millionaire businessman, who was found guilty yesterday of driving a gang of thieves around south London during last summer's riots.

Detective Constable James Quigley, an expert on gangs in south London, is said to have contacted Laura Johnson, 20, shortly before she was due to give evidence at her trial. She alerted her defence barrister who then informed the court.

The messages are not believed to have been sexual in nature, but any contact between police and an accused person before they give evidence could amount to contempt of court. The officer is being investigated by the Metropolitan Police's internal investigations unit and its findings will be reviewed by the trial judge.

The revelation is a remarkable twist in a case that documented how a privileged university student with a history of mental health issues was sucked into last summer's riots as she helped a gang go on a looting spree.

Jurors heard how Johnson became friends with Emmanuel Okubote, a convicted crack dealer and thief, after being introduced to him through a mutual friend. On the evening of 8 August, as riots exploded on the streets of London, she drove to Okubote's house to drop off a phone charger but ended up chauffeuring him, 18-year-old Alexander Elliott-Joahill and a 17-year-old on a looting spree.

With Johnson at the steering wheel, the gang of thieves jumped out and either looted stores or robbed passers-by at knifepoint.

Yesterday a jury convicted Johnson of one count of burglary and one count of handling stolen goods. She was acquitted of stealing cigarettes from a BP garage. The 17-year-old, who cannot be named for legal reasons, was convicted of burglary.

At Inner London Crown Court, trial judge Patricia Lees warned the pair that they faced a custodial sentence. "You have both been convicted of serious offences," she said.

During her testimony, Johnson claimed that she had felt powerless to stop the gang, who she said had jumped into her car wearing hooded tops and balaclavas before ordering her to drive.

She will be sentenced on 3 May.