Bungling metal thieves are believed to have caused a major fire at a disused mill last night.

And a firefighter has warned that people messing about with electrics at derelict buildings are risking their lives.

Emergency services were called to Green Lane in Yeadon at about 8.30pm yesterday, where an oil-filled electrical transformer was abaze by the side of the disused Naylor Jennings dyeworks.

Witnesses saw two men fleeing the scene. Police believe they may have been trying to steal copper from the transformer when it caught on fire and they fled.

Fire crews from Rawdon, Stanningley and Cookridge managed to stop the blaze from spreading to the mill building itself, and a National Grid worker had to come out to help make sure the transformer was isolated from the electricity supply.

A police spokesman said: “We are treating it as an attempted metal theft.

“We would appeal for anyone who saw either of the suspects to contact the Aireborough and Wharfedale Neighbourhood Policing Team, via 101.”

Rawdon fire station watch commander Steven Houldsworth said: “These transformers are full of copper, aluminium and other metals which are of a high value.

“It’s not like a transformer in a house, which is a panel, this thing was about three metres high, three metres wide and three metres deep.

“It would have provided power to a very large mill building. It was a bit like a sub-station.”

He said once the they used foam to put out the oil, which was leaking from the transformer and was on fire.

Mr Houldsworth said in this case, it appeared that the transformer had already been isolated from the grid, and the fire had been set deliberately for some reason.

But he said it was dangerous for people to assume the electrics would be turned off in such derelict buildings.

He said: “It’s quite an important safety message. Sometimes people do get injured when they are messing about in these rooms - and it can prove fatal.”