Harman is fined £400 for driving at 99mph

Harriet Harman, the Solicitor General, was banned from driving for seven days and fined £400 yesterday after she admitted speeding at 99mph on a motorway.

The sentence – which was criticised by the Automobile Association for being too lenient – was issued as it was announced that court fines should be more closely linked to offenders' incomes.

Ms Harman, 52, was said to be taking her son back to Bristol University after the Christmas break when she was stopped on the M4 near Swindon on 8 January.

A spokeswoman for the AA said that considering Ms Harman's salary – £115,989 plus full parliamentary pay – the fine was insufficient. "The fine is on the lenient side compared to what she earns each week, each month, each year. It is less than we would have thought she would get for that particular offence," she said.

Professor Rod Morgan, the chief inspector of probation, told the Home Affairs Select Committee yesterday that the use of fines "has declined disastrously in the last few years".

Ms Harman is a high-ranking minister with the Crown Prosecution Service (CPS). As well as influencing how CPS policies are implemented and how the body is operated, she is deputy chief adviser to the Attorney General. The Attorney General's office refused to comment on the fine.

Colin Meeke, for the prosecution, told North Wiltshire magistrates' court in Chippenham that a laser speed detector recorded Ms Harman driving at 99mph in a 70mph zone.

Representing Ms Harman in her absence, Tim Dixon told the court she was was "extremely sorry". He said: "She was travelling in the outside lane when she approached and overtook a gaggle of HGV vehicles. She thought she was adhering to the speed limit." Mr Dixon said his client had been driving for 26 years without incident and the court heard she had a clean licence.