BOMB disposal experts were forced to carry out a controlled explosion after "potentially hazardous" jars of acid were discovered at a derelict former crisp factory in Bradford.

Officers in the Royal Logistics Corps were called to the former Seabrook Crisps site in Allerton Road yesterday after contractors demolishing the building found jars of picric acid, a substance used in the manufacture of explosives.

The area was evacuated and the road closed in both directions as the substance was detonated in a 10ft deep hole.

Work to clear the site to make way for a new Aldi supermarket began at the start of the month.

Thomas Crompton, managing director of Thomas Crompton Developments Limited, the Bradford-based firm working to demolish the factory, said the substance had been found in a fire-damaged old mill on the premises on Monday night.

"We had taken the roof off and were making a routine inspection and risk assessment when we found the substance," he said.

"It gave us immediate concern so we stopped working and used our consultant chemist who advised us of the dangers.

"He advised we contact the fire brigade and police, so we did."

A Royal Logistics Corps Bomb Disposal vehicle, sent from Catterick Garrison in North Yorkshire, arrived at the scene shortly before 2pm, joining a number of police vehicles parked on one of the forecourts of the building.

Police stood guard at the edge of the cordon to prevent any members of the public gaining access to the site.

At about 3.30pm, the area was cleared to allow the substance to be detonated safely.

"We were moved to an area where we couldn't see the explosion, but we could hear the bang, and the ground shook," said Mr Crompton.

"It is a banned substance, and it was definitely picric acid as it was labelled up.

"It must have been there for many years, but I've no idea what it would have been used for.

"It could have been very dangerous, but the building has been given the all-clear by the bomb squad and work will be re-starting."

Police were involved in sealing off the area before the Army team moved in to carry out the controlled explosion.

"There was no immediate risk to the public," said a spokesman for the force.

When questioned about the incident by the Telegraph & Argus yesterday, a spokesman for Seabrook said the company no longer had any connection to the site and Aldi refused to comment.

The site has been vacant since 2004 and suffered a major arson attack in May last year, which destroyed the third floor and roof of the building.

Councillor Malcolm Sykes (Con, Thornton and Allerton) had spoken of his relief when demolition began, saying he was "surprised" no children had been killed there.

"I said I was surprised no-one had been killed, and this incident just backs that up," he said yesterday.

"It is extremely worrying wondering how long that danger might have been there, it could have been more than ten years, which is frightening.

"Hopefully they will find out who was responsible for putting it there and hit them with the necessary legislation, as it's a criminal act."