A 25-year-old has been arrested over a high-speed motorway crash in which two people were killed and another six injured.
The man, from east London, was held by Hertfordshire Police on suspicion of causing death by dangerous driving after the smash, which happened in the early hours of this morning.
Two BMWs collided on the M1 near Watford in Hertfordshire shortly before 2.40am, killing the driver and rear seat passenger of one of the cars.
Witness Basit Nasir told the Evening Standard that the BMWs "appeared to be having a high-speed race" and had sped past him at around 140mph.
He said: "It was total mayhem. There was mangled metal everywhere. It was foolish of them to drive at this sort of speed. It was raining as well."
Mr Nasir said that four men in a Mercedes arrived at the crash scene and scuffled with survivors.
He told the newspaper: "They all jumped out and everybody started punching each other. They said, 'What have you done? You have killed them.' I tried to break up the fight and called the police from my mobile."
The two men who died have not been named by police but were aged 22 and 24 and both from east London.
Two other passengers in the same car were also hurt and taken to St Mary's Hospital in Paddington, central London, with "serious injuries", Hertfordshire Police said.
Four men travelling in the other BMW also needed hospital treatment for their injuries.
The accident, which happened between junctions five and four, resulted in the closure of five junctions of the motorway in both directions, and the southbound stretch was shut for several hours.
Hertfordshire Police have appealed for witnesses to the crash or the events that led up to it to contact them.
Motorists near Bristol are facing long tailbacks following a fatal crash on the M4.
A lorry driver died in the M4 crash between the vehicle and another HGV close to the Almondsbury Interchange.
Avon and Somerset Police said the eastbound carriageway would be closed for much of the day.
"Police are advising motorists to avoid the area if at all possible as serious congestion is anticipated during the peak period," a force spokesman said.
"All three lanes have been closed to allow emergency services access to the collision.
"Vehicles travelling from the west along the M4 are being urged to use the M49.
"Traffic is advised to avoid the area if at all possible and find alternative routes as the section of the motorway is likely to be closed for a significant part of the day."