Detectives have appealed to the criminal underworld to search their conscience in a bid to catch a dangerous gang of armed robbers who put a bank manager and his family through a terrifying ordeal.

Just over a year ago, John Diggle, manager of the Natwest branch in Bury New Road, Whitefield, was kidnapped with his family at gunpoint and held hostage for two days.

Senior investigating officer in the case, Detective Inspector Simon Collier vowed to catch the gang and appealed to members of the public and any associates of the robbers to come forward with information.

He said: "There are unwritten rules in criminal circles and this case pushes the boundaries. This was a particularly nasty attack on the bank manager and his family, who were put in a life threatening situation. It was a terrible experience for two very young girls and their mum and dad. The case will not close until we catch them."

On September 21 last year, Mr Diggle was at home in Leigh with his wife Lynne and daughters Joanne (14) and Nicola (12).

At around 8pm the girls answered the door to two men who threatened them with a handgun. The men wore ill-fitting suits, false beards and short black wigs.

After getting the family together in the lounge, the raiders bundled them into the family car - a blue Fiat Brava - and Mr Diggle was forced to drive at gunpoint to Schofield Lane in Leigh.

The terrified family were then transferred to a stolen silver grey Renault Megane Scenic, which had its back seats removed, and told to lie on the floor in the back with pillow cases over their heads.

After a 20 to 30 minute drive the family heard the men, who spoke with local accents, mention their location on the walkie talkie as Chequerbent roundabout in Westhoughton.

They were then driven to what is believed to be a warehouse in an unknown location where they were kept overnight, with their wrists bound with plastic ties.

Throughout the night, Mr Diggle (45) was interrogated by the offenders about his job and place of work. His 44-year-old wife and their two daughters were kept under observation and when they wanted to use the toilet, were marched in single file and told to put the pillowcases back over their heads when they had finished.

The following morning, between 6am and 6.30am, the family were driven for 20 minutes from the warehouse to Fountain Place in Whitefield where Mr Diggle's Fiat was waiting.

He was forced to get into his car and follow the Scenic to nearby Elms Community Centre in Green Lane.

Around 8.20am, he was forced to drive one of the offenders to the Natwest and park down the side of the bank near the Metrolink station.

The Scenic, which was carrying his family, followed and parked in the same location for a while as Mr Diggle was ordered to open up.

As five members of staff arrived for work, they were tied to each other with plastic ties and locked in the bank vault. The gunman then fled with a substantial amount of money, believed to be up to £300,000, and escaped in a waiting Megane car.

While the robbery was taking place, Lynne and her daughters were driven to Ringley Old Brow, in Stoneclough and tied to a lamp-post in a remote lane.

At around 9.30am, they managed to escape and raised the alarm at a nearby house.

A short time later the burned out Scenic was found in Park View, behind an Esso garage in Manchester Road, Kearsley and a white two door Renault Clio was found burned out in Sandmere Walk, Blackley.

Police believe that another offender used the Clio during the incident.

A statement issued by Mr Diggle following the incident last year said: "It has left us all extremely traumatised and we will never be able to forget those fearful moments."

Det Insp Collier said: "We believe there are a minimum of three men involved and there may be other members of the gang who only had a peripheral role, such as organising the theft of the vehicles.

"There remains a £50,000 reward for information leading to the conviction of the offenders and I would ask anyone with information, whether they be a member of the public or associates of the offenders, to come forward.

"This was a devastating incident which has changed the lives of the Diggle family."

Detectives are also interested in information about the disused warehouse, where the Diggle family were kept overnight.

It is described as having a white or concrete pillar supporting the roof with a metal bar going through from which hung some coat hangers.

The building also had a window made of small glass cubes and the family could hear the sound of trains, aeroplanes and dripping water while they were kept captive.