A series of brutal armed robberies on supermarkets in Bradford and across West Yorkshire will be investigated by a team of detectives from the region's Major Crime Unit.

The dedicated team is looking into the robberies at Co-op stores and other commercial premises in Bradford, Leeds, Huddersfield and Harrogate.

The move comes after Peter Marks, chief executive of Yorkshire Co-operatives Ltd, demanded action from West Yorkshire Chief Constable Graham Moore after gun-toting gangs struck at seven of his stores in as many weeks.

The latest raid occurred at the Co-op supermarket in Allerton Road, Allerton, on March 15 when three raiders brandishing handguns held up five staff and four shoppers.

Although no one was injured, workers were left traumatised.

Detective Chief Inspector Allan Doherty, head of the Major Crime Unit in Leeds, has met Co-op representatives and detectives working on each case. He said officers from the Force's Operational Support Unit will step up patrols in some of the key areas.

He said detectives would be working with local stores to advise them how they can increase their security and advised staff and customers not to challenge or confront anyone committing an offence.

"We are looking at similarities connecting some of the offences across the county but have no evidence to officially link them at this stage," the detective said.

"We want the public to help us and if they do see anything suspicious outside a store to take down car registration details and descriptions of likely offenders, and ring the police.

"Some people may have witnessed these offences and not yet given written statements. They may have left the store before the police arrived or seen something connected outside the store.

"We would appeal to these people to contact their local police station so that they can be seen by police."

Anyone with any information should ring Crimestoppers on 0800 555 111.