A fire broke out at the set of the latest Harry Potter film at Leavesden Studios when a mock battle got out of control.

Watford firefighters were called to an outdoor film set at about 9pm to deal with a blaze in a mocked up castle.

Watch commander Tony Smith said: "I think they are filming some stunts for the last scene. There is a big battle scene involving a lot of pyrotechnics and explosions.

"There is a mocked up castle made of timber, steel and plastic - somehow it caught alight."

"By the time we got there the on-site fire crew had it pretty well under control - they did a good job.

"We just helped damp it down and inspected the area.

"I didn't see any cast - but there were about 100 crew, who were all evacuated to a marshalling are. They didn't seem too concerned.

"It's hard to say how much damage was caused, because some of it may have been planned as part of the filming.

"Perhaps they got much better footage than they expected."