Here's why you heard an 'air raid siren' in Leeds today

Residents took to social media to query where the noise - which sounded like the notorious World War Two warning system - was coming from.

Leeds factory workers in fight to save pension schemeThe source was Unilever's factory on the Coal Road in Seacroft, and it was part of a test drill.

The siren would be used to warn staff of emergencies such as chemical leaks and explosions at the plant, and it is tested annually.

People living nearby are usually informed by post of when the test is due to take place, and banners are placed around the factory site.

The Unilever factory makes all of the company's deodorants for the UK market, and also supplies European countries.

Flammable substances involved in the manufacture of compressed aerosol products, such as ethanol and LPG, are stored at the site, and so the factory is regulated by the Control of Major Accident Hazards Regulations.

The Leeds site is also a research base for the firm. Around 50 people are employed for products to be tested on, and there are over 100 scientists working there.

250 bottles of deodorant and anti-perspirant are produced every minute.