An American servicewoman caught drink-driving in Newmarket after she was seen swerving along the road has been banned from getting behind the wheel for 16 months.

Katelynn Cox, 24, was driving a green Honda Accord around 2.15am on Sunday, June 12, along Fordham Road in Newmarket when she was seen by police, magistrates in Ipswich heard.

The car was described as "swerving within its own lane" and was exceeding the 30mph speed limit by travelling at an estimated 45mph, Colette Harper, prosecuting, told Suffolk Magistrates' Court.

Officers stopped the car due to the manner of driving and found Cox behind the wheel and another passenger in the vehicle, Mrs Harper said.

Police smelt alcohol and a roadside breath test proved positive, the court heard.

Cox was arrested and taken to the police station where it was discovered she was not insured to drive the vehicle.

She blew 59 microgrammes of alcohol in 100 millilitres of breath at the station, exceeding the legal limit of 35mcg in 100ml of breath.

Cox, of Tulyar Walk, Newmarket, had no previous convictions, the court heard.

She pleaded guilty to charges of drink-driving and driving without insurance before magistrates on Tuesday.

David Allan, mitigating, said the offences arose from Cox "attempting to act as a good Samaritan".

He said Cox, who is an intelligence analyst with the United States Air Force (USAF), had travelled back on the train to Newmarket with her partner.

Mr Allan said Cox realised her partner had consumed too much alcohol, so had offered to drive the short distance back to their home in his car.

"She felt she was alright to drive but he plainly wasn't," Mr Allan said. "She offered to make the journey in his car because of the state he was in.

"Good intentions of course but unfortunately ones that have resulted in her ending up in court today."

As well as the 16-month driving ban, magistrates also fined Cox £500 and ordered her to pay £105 in court costs and a victim surcharge of £50.

No separate penalty was imposed for the no insurance offence and Cox was offered the opportunity to take the drink-drive rehabilitation course, which will reduce her ban by 16 weeks if completed.