A cannabis factory', with a street value of about £500,000, was discovered by chance as emergency services investigated a gas blast which had destroyed a bungalow.

Hundreds of cannabis plants were found in an adjoining house as firefighters and police warned people to switch off their power supplies following the explosion in Bradford.

The bungalow, which was empty at the time, was blown into a garden by the blast at Melbourne Place, Little Horton, believed to have been sparked by the theft of copper piping from outside the premises, on Sunday. Nobody was injured.

Police were alerting neighbours when they discovered the cannabis plants in all 16 rooms of a property close by.

Officers seized 600 plants and said there was evidence another 1,000 had already been harvested. The cannabis is thought to have been worth £500,000.

Police said it was a major harvesting operation, which was discovered by chance and had no connection with the explosion.

Forensic inquiries into the find are continuing and police are anxious to trace a man and woman from the adjoining property who have not been seen since the incident.