Harriet Harman, deputy leader of the Labour Party, has received a fine of £350 after pleading guilty to driving without due care and attention.
Ms Harman has had three points added to her driving licence, having reversed her Rover 75 into a parked car while using her mobile phone in Camberwell last July.
However, a second charge of driving while using a mobile phone was withdrawn.
The House of Commons leader and equality minister has now amassed a total of nine points on her licence, the first six coming from a speeding charges in 2007 and 2008.
Motorists with 12 points face a driving ban.