Firefighters believe a grain store could have turned into a giant 'compost heap', which caused a major blaze at a Norfolk farm.

Investigations into the cause of a huge fire in Roudham, near Thetford, were hampered today as crews were forced to return to the scene of Thursday's blaze to dampen down the burnt out warehouse.

However, investigators from Norfolk Fire and Rescue Service believe the spark for the blaze could have come from the tonnes of grain and potato crisps stored in the 3,800sqm building at Camp Farm.

A spokesman for the service said: 'We are looking into the possibility of self heating, like a compost heap, but investigations are continuing.'

Three crews from East Harling, Thetford, and Attleborough fire stations were called back to the industrial estate just before midday to dampen down hotspots following the blaze that destroyed tonnes of animal feed, grain and farm machinery.

The fire service spokesman added: 'It is not unusual to revisit with incidents like these. Some of the potato crisps are smouldering and crews used hose real jets to dampen down to keep the hotspots under control.'

Firefighters managed to stop the warehouse from collapsing and investigations into the cause of the blaze will start when it is safe for officers to enter.

At the height of the fire a large plume of smoke could be seen from miles around. Eighteen fire engines with 80 firefighters from across Norfolk and Suffolk tackled the flames.

Electricity also had to be cut to 85 homes in Roudham and Bridgham for several hours. Thirty farm workers were evacuated from the site, but no one was injured.

Paul Rackham, who runs Camp Farm, spoke of his 'heartbreak' on Thursday and said that he had lost 2,500 tonnes of grain during the blaze, which sells at �200 a tonne, and equipment stored in the warehouse including a combine harvester and trailers.

It was the first time the farmer has had a fire on his property in Roudham Road in 15 years.

Work returned to normal at the industrial site in Roudham today, which is made up of 15 warehouse buildings. The cordoned off store is to the rear of the site.