A policeman on the scene when an entire family was killed in a horrific car crash has described "the worst day of my career".

Sgt Peter Jell, 44, and six colleagues have picked up a police commendation for their investigation into the seven-vehicle crash on the A34 near Bletchingdon in July 2006.

Sgt Jell and his roads policing team from Bicester had to deal with the harrowing aftermath of the crash.

And their painstaking 18-month investigation led to the jailing of lorry driver Ian King, 61, in a landmark conviction.

Sgt Jell said he would remember forever arriving at the chaos of the crash where one vehicle was crushed under a lorry.

He said: "You could see a small piece of metal underneath the cab of Ian King's lorry. The boot was in effect the roof — it had been folded in half.

"We immediately knew it was a fatality, but we didn't know how many."

Police contacted colleagues at Staffordshire Police to locate the family after tracing the number plate.

Sgt Jell added: "About five hours later we got a call back to tell us the whole family was in the car.

"We were on the busy A34 and there were police, ambulance and fire crews all around — when the news filtered through the whole place went silent.

"In 26 years with Thames Valley, and 14 on traffic, it was the worst day of my career without a doubt."

It took emergency services another four hours to release the bodies and the A34 was virtually shut down to all traffic for 18 hours.

Malcolm Dowling, 46, his wife Janice, 42, and their sons Richard, 16, and George, 11, from Lichfield in Staffordshire, all died in the crash.

Hours were spent reconstructing the crash to discover what happened.

The team proved King's lorry struck a Renault Laguna sending it up in the air into the second tier of a stationary car transporter.

King's lorry then crushed the Dowling family's Peugeot 306.

The lorry's tachographs showed King did not brake and must have been asleep.

King, of Leicestershire, denied four counts of death by dangerous driving claiming he suffered sleep apnea — which meant he would have fallen asleep without being aware of it.

But, in a landmark case at Oxford Crown Court, earlier this year police achieved the first successful conviction against the defence of sleep apnea by proving the defendant would have been aware he was tired.

King was jailed for three years and nine months and banned from driving for five years.

Sgt Jell added: "It was an incredibly harrowing experience to deal with, but we wanted to make sure we got a result.

"It was something out of the ordinary and something we all worked very hard on."

He added: "I am very proud to receive recognition. All I've ever wanted is for, at the end of the investigation, to say to the family 'I've done my best'.

"Hopefully I'll never deal with anything like this again."

Chief Constable's Commendations were also presented to Pcs Richard Ell, Sarah Holmwood, Richard Medway and David Rose, family liaison officer Pc Gai Palmer and Deborah Garrett of the Crown Prosecution Service.