Simon Elbrow was driving his wife Louise, 37, and children Olivia, three, Thomas, six, and eight-year-old William from their home in Thrapston for a weekend at the seaside on May 4 last year when tragedy struck, Cambridge Crown Court heard.

Mr Elbrow, 38, described how he had been at the wheel of a Mitsubishi 4x4 and was towing the family caravan when he slowed down behind other traffic queuing on the A14 eastbound past the Stow-cum-Quy turn in Cambridgeshire.

The truck in front came to a stop and put its hazard lights on, and he did the same.

He said: "I looked in the rear view mirror and saw a lorry heading towards us. I did a double-take and immediately looked to Louise and said: "That lorry is not going to stop.

"It was about four to five hundred yards away. I tried to ditch my vehicle – to drive off the road to my left on to the verge. I looked in my mirror again and within what seemed like a millisecond there was a thump."

He said what happened after was a blur.

Lorry driver Michael Coombes, 62, from Stowmarket, denies the charge of causing William's death by dangerous driving.

It is alleged while other traffic slowed in response to a broken-down lorry ahead, Coombes failed to brake and then hit the Elbrows' caravan.

The jury has heard tachograph records from other lorries caught in the queue showed they took at least 30 seconds slowing their vehicles in response to the tail-back and obstruction up ahead.

But Coombes' tachograph is alleged to have shown no slow-down and that he hit the Elbrows' caravan at about 55mph.

The court has heard that the family's caravan was smashed to smithereens and the 4x4 was pushed into the back of the HGV ahead. William was killed and Mr Elbrow was seriously injured.

Other motorists were also injured as Coombes' lorry swerved into the outside lane, hitting a van in the queue and causing corresponding shunts.

The road was closed for 10 hours.

The case continues today.