Two brothers who used their printing firm's Christmas and New Year break to churn out £1.2 million worth of fake banknotes have both been jailed for seven years.
Apparently respectable businessmen Amrit and Prem Karra acted as "masterminds and architects" of the highly-sophisticated counterfeiting operation, Birmingham Crown Court heard.
Sentencing the brothers and two other men who also took part in the scam, Judge Richard Bond said such offences undermined the integrity of the UK's financial system.
The Karra brothers and their brothers-in-law, Rajiv Kumar and Yash Mahey, were all convicted of conspiracy to produce counterfeit notes following a five-week trial which ended in December.
The trial heard Amrit Karra, of Broadway North, Walsall; Prem Karra, of Brookhouse Road, Walsall; Kumar, of Clarkes Lane, West Bromwich; and Mahey, of Cranbrook Road, Handsworth, Birmingham, even worked through the night to print fake £10 notes with a face value of at least £1.27 million.
Amrit Karra, aged 45, Prem Karra, 43, Kumar, 40, and Mahey, 44, used specialist paper, inks and foil to run off the near-perfect forgeries at a print-works in Hockley, Birmingham.
"In this case the amount of money produced and disseminated into general circulation was enormous.
"Production of counterfeit notes undermines the whole economy of the country... essentially it undermines the whole integrity of the currency system.
"It is so serious that only lengthy custodial sentences can be justified."
Jailing both Mahey and Kumar for four-and-a-half years, and barring the Karra brothers from acting as company directors, Judge Bond said the offences were motivated by greed.
He told the defendants: "All four of you knew what would happen to the notes.
"You knew that if you were caught it would affect your wives and your children and other members of your immediate family.
"Knowing, as you did, the consequences of being caught, you ignored your families. The risks taken in this case were high and you must personally take the blame."
The National Crime Agency (NCA) said Karra Design and Print had legitimate business contracts but the four men had used the firm's computers and machinery to counterfeit notes in late 2010 and early 2011.
The vast majority of the "extremely high quality" notes even had individual serial numbers, and were only identified as fakes as they were sorted by banks to be loaded into cash machines.
Although the notes' holograms were easily identifiable as bogus, the other security features were so convincing that only 10% of them were spotted by members of the public.
In a statement issued after the case, the NCA said forensic analysis of the printing firm's equipment showed exactly when it was being used and what was being produced.
Mobile phone data and automatic number plate recognition evidence were also critical to the success of the investigation, an NCA spokesman said.
Lawyers for the Karra brothers argued that the conspiracy was a response to financial trouble at the printing firm.
David Emanuel, defending Prem Karra, described the "one-off" printing of counterfeit notes as a very misguided attempt to save the business, and said his client was someone who had been highly regarded within the local business community.
Franco Tizzano, defending Amrit Karra, told the court during mitigation: "It is a great tragedy that someone with such positive qualities, who has worked all his adult life and was very committed to his family, finds himself before the court."
The fake notes have been found all over the country but the most significantly affected areas were the West Midlands, London and Kent.
Richard Warner, NCA Birmingham Branch Commander, said: "These men ran a sophisticated operation that posed a significant threat to the UK economy at the time.
"By working closely with industry experts our officers stopped them causing more damage.
"Counterfeiting is not a victimless crime. It takes money out of the pockets of individuals and businesses."
A Bank of England spokesperson said: "The Bank works closely with the National Crime Agency in the fight against counterfeiting. We are grateful for their work in pursuing this case to a successful conclusion.
"Those individuals who engage in counterfeiting should know they will be found and punished for their crimes."