For several years people in the Fulwood area have been puzzled by a sound they describe as "like an air raid warning", which sounds every Friday at 9.30am.

Some have contacted environmental health officers, while others have remained mystified as to the meaning of the warning.

George Bettess of Queens Drive said: "My neighbour first drew my attention to it. It is spot on 9.30 every Friday.

"They made inquiries with the police, who didn't know what it was and I spoke to colleagues in the County Council emergency planning department, but they didn't seem to know either.

"We don't think it is to do with the emergency organisations and it's not harming anyone – but we don't know what it is.

"It is really loud and it seems like it is going on for ages, but it is probably over in about 30 seconds. If it is a public warning, what are they warning us about?"

The LEP referred the matter to Preston City Council's environmental health department but officers were puzzled.

A council spokesman said: "We haven't had any complaints about it but we don't know where it is coming from. We're baffled."

Happily, a spokesman from Fulwood Barracks was able to solve the mystery. He said: "Anyone who lives around the barracks will know we test our alarm system every Friday morning."