The gang made off with a total of £360,000 during two audacious raids but were foiled in their third attempt.
The balaclava-clad robbers – brandishing a silver handgun and a crowbar – targeted a Derbyshire branch of RBS by hiding in the roof area and lying in wait for staff to arrive.
They then threatened the workers and tied them up before making off with the cash.
Jordan Lydon acted as a getaway driver for the masked robbers but, despite being jailed, has refused to give their names to detectives.
Lydon – the stepson of a prolific robber – was locked up for nine years after admitting a charge of conspiracy to rob and an offence under the Contempt of Court Act for refusing to identify the raiders.
The gang also stole £250,000 from a TSB bank in Bridlington. A third planned robbery at the RBS in Darley Dale last August was foiled after staff noticed a leak in the roof where tiles had been removed to gain entry.
None of the money has been recovered and now police are appealing for information to catch the pair.
The balaclava-clad robbers – who were brandishing a silver handgun and a crowbar – hid in the roof area of the Hathersage RBS in Main Road on the morning of February 20 last year and lay in wait for unsuspecting staff to arrive before jumping down, threatening them and tying them up.
Lydon’s trial at Hull Crown Court heard Rachael Peters, a customer services officer at the bank, deactivated the alarm and an internal door “suddenly burst open and two masked men appeared”.
She said: “As the door burst open, one of the men shouted ‘don’t scream’.”
Ms Peters did as she was told and the raider with the crowbar ordered her colleague, James Bean, to lie down. His hands were tied behind his back as he lay on the floor.
She “at first thought it was some kind of a joke” but realised that “it was for real” and so “complied with everything they said”.
One of the raiders said he hoped the staff had not got any personal alarms on them and the robber with the gun said: “Let’s start with the ATM.”
Manager Claire Howarth deactivated an alarm. One of the raiders said: “We are not here to hurt you. We won’t hurt you if you do everything we say. If you don’t, we’ll shoot a hole in his (Mr Bean’s) spine.”
Ms Peters told the court: “The cash machine was completely empty in a matter of a few moments.”
One of the raiders then said: “Let’s do the safe now.”
The terrified workers were tied up with cable around their wrists and ordered to kneel down.
One of the robbers told the staff: “You’re not to make a noise for ten minutes after we leave.”
They were warned: “If you make a noise, I’ll come to get you.”
The staff were left in the safe and remained in there “for what seemed like ages” before they heard the sound of doors.
The raiders made off with £108,000 in a holdall.
The court heard Lydon was tracked down by applications on his mobile phone. He was unaware the applications could triangulate his position to phone masts, even when his mobile was not used, placing him near the scene.
Barrister John Thackray said Lydon, of Cleethorpes, was a dad-of-two who was not content with a life of crime and had been corrupted by others.
Sentencing Lydon, judge Mark Bury said: “You were out of your depth – but you seemed to play your own role in this.”
His stepfather Michael Lydon, 51, of Grimsby, who was accused of masterminding the bank raids, was cleared.
He had previously served 18 years after being convicted of another conspiracy to steal more than £260,000 from post offices, shops and a bank in Sheffield, Nottingham, Grimsby and Hull.
Speaking after the case, Chief Inspector Matthew Baldwin, of Humberside police, said. “My main thoughts are with those bank staff who were put through a terrifying ordeal and have been to court again to relieve the experience through a trial.
“We completed the investigation as thoroughly as we could – sometimes you don’t get all the pieces of the jigsaw.
“Ultimately the not guilty verdict in the case of Michael Lydon is a matter for the jury.
“There are no other immediate lines of inquiry to follow in terms of other suspects.
“If new information does come to light it will be investigated.”
Chief Inspector Richard Smith, of Derbyshire police, said “This has been a lengthy investigation and our thoughts are with the bank staff, who were put through a terrifying ordeal which they will never forget.
“But with help from our colleagues in Humberside, one of the offenders is now serving a significant custodial sentence, which will hopefully give them some peace of mind.
“However, there are still outstanding offenders and although there are no immediate further lines of enquiry, we would urge anyone who has any information to come forward so that it can be investigated fully.”
Anyone with information or anyone who knows the identities of the robbers should call police on 101.
• Thanks to the Grimsby Telegraph for assisting in the reporting of this story