Two carjackers have been locked up after they repeatedly rammed police vehicles while trying to escape on a motorway.

Mouctar and Alpha Diallo fled along the M2 from Chatham and onto the A2 before reaching a slip road at the Darenth Interchange junction with the M25.

Mouctar Diallo, a former university engineering student, rammed two patrol cars three times with a stolen Vauxhall Vectra as attempts were made to box it in.

The 21-year-old and his cousin, 17, had stolen the car in a knifepoint robbery.

It happened after the car was advertised on Gumtree for £1,700 and a test drive was arranged.

Alpha Diallo pulled out a knife and forced the seller out of the car when an offer of £1,000 was refused.

Police spotted the car on the London-bound carriageway of the M2 in the early evening on January 3 this year, Maidstone Crown Court was told.

The car was chased for almost 20 miles. At one point it left the A2 at Ebbsfleet, and circled a roundabout before rejoining the carriageway.

Mouctar Diallo rammed the police cars before they were able to force the Vectra into a crash barrier. Diallo fled on foot, but was caught.

He told officers he "just made a bad decision” adding: “I even brought the money to buy the car."

The Vectra was written off and the cost of repairs to the patrol cars ran into thousands of pounds.

Mouctar Diallo, from South Norwood, south east London, admitted robbery and dangerous driving and was jailed for three years. He was banned from driving for 33 months.

Alpha Diallo, from Mitcham, Surrey, admitted robbery and threatening with a blade. He was sentenced to a two-year detention and training order.

Passing sentence, Recorder Cairns Nelson QC said: "This was a knifepoint robbery of a gentleman who was helping his friend to sell a car. He was taken off on a test drive and his instructions were ignored.

“It was dark and it must have been very frightening for him. You, Alpha Diallo, with the knowledge of Mouctar Diallo, produced a knife, threatened him with it and by such means you robbed him of the car.

"There was then a lengthy police chase in which you tried to get away, driving extremely dangerously and recklessly, endangering other road users."

After sentencing, DC Mark Donovan said: "This was undoubtedly a terrifying experience for the victim. Fortunately, it was resolved without any injury to him or to the wider public who were put at risk by Mouctar’s dangerous driving.

"While the vast majority of sales of goods and vehicles arranged online are done so safely, it’s important to take some safety precautions.

"In cases where you intend to meet a buyer or seller in person, take someone with you, meet in a public place during the day, and where possible avoid carrying large amounts of cash."