Twenty people died and nearly 500 others were sick in the outbreak, which started in November 1996 when pensioners became ill after a church lunch in Wishaw, central Scotland.

Paul Santoni: "Families want the truth"

Lawyer Paul Santoni, representing families of several of the victims, said: "We want to find out what happened, how it happened, how it came to be so massively widespread and why the authorities were so slow in putting a cap on it.

"We simply want the truth. If we get that, we will be absolutely delighted."

The fatal accident inquiry - similar to an inquest - is being held in a church in Motherwell, Lanarkshire, and is expected to last three months.

It will hear from more than 100 witnesses, including those who fell ill, authorities who tried to stop the outbreak and medical officials who treated the victims.

Pensioner Harry Shaw, 80, was the first person to die. Another 19 people, most of them elderly and from a wide area of central Scotland, died in the following seven months and 496 others fell ill.

The infection has already led to widespread changes in the food industry.

Following the tragedy the government set up a report under Professor Hugh Pennington, which led to the creation of a national Food Safety Agency.

The case against John Barr collapsed through lack of evidence

John Barr, the Wishaw butcher who supplied the meat for the church lunch, was tried at Hamilton Crown Court for culpable and reckless conduct over the supply of cooked meat. He was cleared when the case collapsed.

However, in January this year his firm was fined �2,250 over food hygiene charges arising from the outbreak.

It was alleged that the shop's back premises showed traces of E. coli 0157 bacteria on a boiler used for cooked meat and on a vacuum packaging machine.