Kidston, known for her colourful prints and whose designs have been worn by Prince George, apologised for the incident and admitted she had committed the offence of driving while using a hand-held mobile phone.
At Lavender Hill magisrates court on Wednesday, she was found guilty and her case was adjourned for a sentencing hearing next month.
The designer already has six points on her licence, and is now facing a ban as the mobile phone offence usually carries a further six points.
Kidston apologised at the roadside after she was pulled over by PC Paul Craven at 3.45pm on January 31. “Yes. I admit I looking at my phone on the seat”, she said, in a written guilty plea seen by the Standard.
“I had been in a long stationary traffic jam and looked at a message as the traffic started to move. I apologise.”
The incident happened in West Carriage Drive as she drove through Hyde Park.
“I saw a blue Mercedes Benz queueing in slow moving traffic”, said PC Craven.
“I noticed that the driver of this vehicle was using a hand-held mobile device with an illuminated screen while driving. The device was being held in their left hand in front of themselves.
“The driver did appear to be operating the device with her right hand.
“I stopped the vehicle and spoke with the driver. I confirmed they weren’t making emergency contact to the 999 service.
“I pointed out the offence where they confirmed the communication was checking a message.”
The officer recorded Kidston as saying “I apologise”.
Court papers show the designer initially paid a fine over the incident, but legal proceedings under the Single Justice Procedure were initiated as she already had six penalty points on her licence.
Prosecutor Abigail Akano said Kidston was previously convicted twice in May last year for speeding offences, receiving three points in each case.
Letters were sent to Kidston’s £4 million Kensington home, and her case was moved to open court this week to clarify her guilty plea.
In a further letter to the court, Kidston asked for the case to be settled in her absence.
“I had asked that the fact I was sitting in traffic at the time be taken into account”, she said. “I appreciate it’s not a valid excuse to have looked at my telephone.”
Magistrates adjourned the sentencing hearing until October 18 so that Kidston could be formally told she now faces a ban.