A G4S employee who sent an anonymous letter threatening to blow up vans and demanding £1m from the firm issued an apology to colleagues from court before he was locked up for two years for blackmail.

Daniel Garland, 20, caused work to halt at the cash-handling depot in Thornaby when he posted the chilling note in January saying he had planted remotely-controlled “mini-bombs” on vehicles.

More than 100 police officers joined a major inquiry across four force areas, cash-in-transit vans were recalled to the depots to be searched and the security giant’s losses were put at £15,000.

The police operation was estimated to have cost a further £35,000.

Garland, from Durham Place, Chester-le-Street, had admitted a bomb hoax charge and was convicted after a trial of a blackmail offence.

Before he was sentenced to two years in a Young Offenders’ Institution, Garland read out a letter via a videolink from prison.

Garland said: “I would like to express my heartfelt apologies to the Crown, members of G4S, the police and any individuals that might have been affected by my mindless and thoughtless actions.”

Sentencing at Durham Crown Court, Recorder Euan Duff said: “We live in an age when bombs which can kill or maim are sadly a feature of modern life in the UK.

“No bomb threat can be taken lightly.”

The judge accepted Garland never truly intended to make £1m from the letter, but said his intention was to get two colleagues into trouble.

The anonymous letter, which Garland took pains not to touch without gloves, said the two were involved in an earlier, unsolved robbery on a cash-in-transit van.

Garland claimed during trial that he had been bullied by them at work, but the judge dismissed that.

He believed they might lose their jobs as a result of his plot.

Nicole Horton, defending, said he was immature and naive.

She said: “This was a badly-thought-out piece of revenge, clearly he never intended to make himself a financial gain.”

He has been on remand since he was convicted of blackmail and Miss Norton said: “Daniel has had the shock of his life in going into prison and has found it an extremely distressing experience.”

At the trial, the jury was told how branch manager Dean Jeffels was terrified when he read the letter, which said robbers would storm the depot with weapons if £1m was not loaded on to a truck the next day.

It also warned of visiting a mother and her newborn baby while her partner – a G4S employee – was at work.

Speaking afterwards, Assistant Chief Constable Adrian Roberts, from Cleveland Police, said: “I am pleased with the sentence handed to Mr Garland at court today.

"Whilst we now know that he had no intention of carrying out his threats, the letter he sent resulted in serious disruption to the G4S business, significant anxiety to its staff and necessitated a massive police operation.

“This was a clear case of blackmail – a demand for £1m was made and a series of serious threats were made in the letter to reinforce the demand.

"This included threats to cause explosions to company vehicles and those of employees, to attend the company depot with firearms to secure the money and to harm an employee’s partner and newborn baby. This was backed up with clear warnings around not contacting the police.

“Whilst these cases are highly unusual, the demand letter was credible, revealing detailed knowledge of company operations, employees and vehicles and, crucially, apparent knowledge of a robbery committed on a G4S cash van in the area the previous month, for which suspects had not been identified.

“Mr Garland must have known that G4S and the police would have had no option but to take radical action to secure the safety of the public and G4S employees. The G4S depot was effectively ‘locked down’ and a massive police operation was launched across four forces to simultaneously secure and search the significant number of vehicles and premises connected with the threat.

“Regardless of Mr Garland’s ultimate intention, it would have been clear to anyone making such serious threats that massive disruption would be caused to the business and that this would cause both significant concern to company employees and financial detriment to the company.

“The magnitude of Mr Garland’s offending has been recognised and I hope he now realises the scale and impact of his actions.”