FOUR firefighters were feared dead last night after a suspected arson attack on a warehouse. It was the fire service's worst single loss of life since the Kilbirnie Street disaster in Glasgow 35 years ago.

The tragedy happened after an inferno ripped through a vegetable packing plant in Atherstone on Stour, Warwickshire, at 6pm on Friday. As many as 100 firefighters from four counties tackled the blaze overnight before it was put out 12 hours later, early yesterday .

One crew member was pulled from the building and died in hospital and three others remained unaccounted for last night. The fire brought down a large section of roofing.

Prime minister Gordon Brown said in a statement he was "shocked and saddened" and his thoughts lay with the families of the dead, missing and injured. He added: "I pay tribute to the courage, dedication and service of the firefighters. We stand ready to help in any way we can."

The Fire Brigades Union (FBU) described it as its worst single loss since seven men perished tackling a fire which broke out in the attic of a cash-and-carry textile warehouse in Glasgow on August 25, 1972. General secretary Matt Wrack said: "This could be the worst loss the fire service has faced in decades. Our service is traumatised by what has happened."

Warwickshire county fire officer, William Brown, a firefighter for 33 years, said the incident was the "worst day of my career" and expressed "grave concerns" over the missing crew's fate. He said: "This is a tragic event and our hearts and thoughts go out to those who have been affected by it, the family of the people who have suffered, and also their colleagues.

"The fire service has a strong family tradition - it is a close bond which allows us to do our work, often in difficult and sometimes in dangerous circumstances. The firefighters were heroically doing their job."

The known victim has not yet been named publicly. The police and fire service are undertaking a joint investigation into the fire and their own response to it.

Once the building is safe enough, forensic experts from the police and fire brigade will begin work to establish the cause. Police also launched an appeal for witnesses who may have seen anyone acting suspiciously in the vicinity of the plant between 5pm and 6pm on Friday.

Brown said his brigade's inquiry will examine the "tactical decisions" taken by senior officers to send the crew into the building to look for survivors after staff inside the plant escaped unhurt.

He added: "Our firefighters are trained to make a decision as soon as they arrive. The tactical decision of the officer in charge, the first person to turn up, is the decision they make based on their risk assessment. The whole situation around this incident, the tactics employed will all be subject to the investigation.

"I wouldn't like to speculate on what was found in that building and what has generated so much heat in that building. Our investigation will unravel this whole thing ... and the reason why there was such a catastrophic fire."

Bill Holland, the assistant chief constable of Warwickshire Police, said: "The fire is being treated as suspicious. A joint investigation will commence when the fire is out and it is safe to enter the premises, involving specialists from the fire service, police force and forensic experts."

Conservative leader David Cameron added: "This tragic incident is another reminder of the dangers the emergency services put themselves in day in day out to ensure the safety of the public."

The FBU is concerned over the rising numbers of firefighters who have died tackling incidents, with at least 12 deaths in England over the last decade.

In 1972, seven firefighters died while fighting a blaze at a warehouse in Kilbirnie Street, Glasgow. Six firemen, led by Andrew "Paddy" Quinn perished as they attempted to rescue colleague James Rook, who also died in the blaze.

The firefighters are honoured at a memorial in the Necropolis cemetery in Glasgow which also contains the names of 14 firefighters who perished tackling a fire at a whisky bond in the city in 1960.