A teenage driver who admitted she could have been day dreaming when she smashed into the back of a stationary car on a motorway, killing a grandmother, has been locked up for two years.

Chloe Thompson was speeding at 80-88mph in her Smart Forfour car on the M25 when she crashed into 71-year-old Anne Tongs’ Citroen C4.

Maidstone Crown Court heard Thompson was 18 and had only been driving for about four months before the tragedy happened on June 3 last year at about 6pm.

It was aftewards discovered she was suffering from ADHD, which could cause poor attention and focus, and “distractability”.

Thompson, of Carlton Road, Eastbourne, east Sussex, admitted causing death by dangerous driving. She was banned from driving for six years.

A care home worker, looking after dementia patients, she was on her way to see her father in Hertfordshire with her boyfriend.

She was heading towards the Dartford crossing near Swanley for the junction three turn off.

Prosecutor Siobhan Molloy said the collision was captured on the dash cam of a car travelling in the same direction.

Thompson would have passed signs warning of congestion across all three lanes and advisory speeds of 50mph and 40mph about one-and-a-half miles before the scene of the accident.

Miss Molloy said Mrs Tongs, from Southend, had slowed down and stopped because of the build-up in traffic.

Her brake lights were on for five to seven seconds before Thompson approached.

“She doesn’t slow down and doesn’t brake at all,” says Miss Molloy.

“Her car impacted with the back of Mrs Tongs’ car at a speed of 80-88mph.

“The impact forced Mrs Tongs’ car into the back of a Vauxhall Insignia in front and then into the back of a BMW.”

The victim, who did voluntary work for Red Cross, was pronounced dead at the scene. There were no other major injuries.

Miss Molloy said Thompson was a relatively inexperienced driver, having passed her test in January last year.

When interviewed she claimed her satnav had stated she was doing about 74mph before the crash.

“She recalled seeing brake lights but almost instantaneously collided with the Citroen,” said Miss Molloy.

“She said she looks at signs on the motorway but doesn’t really take on board what they show. She recalled a 40mph sign but didn’t know where.

“She described motorway driving as tedious and says it all looks the same, so her attention can be lost. She said she just wanted to get to her dad’s a bit quicker.

“Her attention was drawn to the scenery or she was just having a daydream. She liked looking at the trees. She said it was her fault she didn’t realise she was going too fast.”

Judge Charles Macdonald QC said he found Thompson was speeding at about 85mph at the time of the collision.

If she had been keeping a lookout 177 meters from the crash, he said, she could have avoided it completely.

“The dangerous driving had four aspects,” the judge continued.

“First, prolonged bad lookout; second, short-term bad lookout; third, a speed of 15mph over the limit; fourth, a speed of about 45mph over the advisory limit.”

A psychiatrist diagnosed Thompson with ADHD on January 10 this year and suggested her “bad lookout” could have been caused by the condition.

“Inexperience played no part in this collision so far as lookout is concerned,” said Judge Macdonald.

“All cases of this sort are tragic - tragic for the family of the deceased and for the driver who must live with what she has done. Nothing brings back the deceased.

“The sentence doesn’t place a value on life, nor should it, and it isn’t a case for revenge.”

Thompson will serve a year of youth custody before being released on licence.

Detective Constable David Holmes, the investigating officer for the case, said: "Thompson was travelling in excess of the enforced speed limit, however, she was also around 40mph in excess of the advisory speed limit.

"While it may only be an ‘advisory speed’ people must take heed in the fact that it is shown for a reason, along with the overhead gantries warning of queues ahead.

"It is important for all drivers to be aware and concentrate at all times when driving, especially on fast roads and especially those less experienced drivers who have recently passed their driving test.

"This needs to serve as a reminder of the tragic consequences that can occur when concentration is lacking and important information is ignored.

"While Miss Thompson did not set out to kill, the victim has tragically lost her life when she herself was safely negotiating the road and hazards presented to her, unbeknown of what was going to happen."