The jury in the Simon Jones docks accident case were told the chances of such a tragedy happening were 'infinitesimal'.

Sussex University student Simon, 24, was killed instantly when a two-tonne grab snapped shut on his head while unloading a vessel at Shoreham Harbour.

But in his closing speech the barrister representing 59-year-old Richard Martell, the boss of Dutch shipping firm Euromin Ltd, told jurors he should not be found criminally responsible for the accident.

Robert Walker said a combination of unforeseen circumstances came together at the same time.

He said his client was accused of manslaughter on the basis of what "could have been done" to prevent the accident.

Mr Jones had been working beneath the jaws of the clamshell grab during his first day as a casual labourer to earn cash during the Easter holidays in 1998.

Along with Sean Currie, an experienced worker, he had been unloading bags of building stone from the hold on to chains suspended below the open grab, the Old Bailey heard.

Mr Walker said: "For some reason the grab was being lowered too far. Sean Currie failed to communicate this to the crane operator."

It is thought crane driver Jim Harris may have accidentally nudged the lever which operates the grab.

Mr Walker said: "Mr Harris's actions have remained unexplained. He operated the lever which closed the grab and did so at the very moment Simon Jones was reaching under it to attach a bag of cargo to the chain.

"What are the chances of that combination of circumstances coming together at that moment? In our submission they are infinitesimal."

Martell, of Jubilee House, Aldingbourne Drive, Crocker Hill, Chichester, denies a charge of manslaughter on April 24, 1998.

Dutch-owned Euromin Ltd, of the Glassmill, Battersea Bridge Road, London, denies manslaughter and six charges under Health and Safety regulations.

The trial continues.