A jury trying a man over the deaths of two firemen following a huge explosion at his family-run fireworks factory retired to consider its verdicts for a fourth day today.

Nathan Winter, 25, is accused of two counts of manslaughter after retained firefighter Geoff Wicker, 49, and support officer Brian Wembridge, 63, were killed in the blast at Festival Fireworks UK Ltd at Marlie Farm in Shortgate, near Lewes, East Sussex.

His father, company owner Martin Winter, 52, was found guilty of the charges on Monday while the jury also found the firm, now called Alpha Fireworks Ltd, guilty of two counts of breaching health and safety legislation.

As well as killing the two firemen, both long-serving members of East Sussex Fire and Rescue Service, the blast on December 3 2006 injured some 20 others, mainly police and fire officers.

Jurors at Lewes Crown Court heard that Martin Winter was "grossly negligent" as he knew an unlicensed metal container packed with fireworks could explode if a blaze broke out.

Prosecutors alleged that Nathan Winter was also familiar with the different hazard classifications given to fireworks and their potential for mass explosion in a confined steel container.

The father and son, who live on Marlie Farm, both denied two counts of manslaughter.

During his defence case, jurors were told that Nathan Winter could not be considered responsible for the two deaths as it was the duty of fire officers at the scene to be aware of the dangers of a blaze involving fireworks and to take the necessary precautions.

It was also suggested during his evidence that his repeated warnings to keep the flames away from the container were not taken seriously enough by fire officers.