Phillip Brown, 44, and Christian Brown, 34, who ran the commercial printing firm, together with Mehmet Altinfincan, 27, were the key players in a counterfeiting operation that printed fake £20 notes worth more than £17.5m.

Phillip and Christian Brown, who were joined by their cousin Daniel Brown, a 33-year-old former city trader, in the dock at Kingston Crown Court on Tuesday (5 April), were both handed nine-and-a-half year sentences for conspiracy to make and deliver counterfeit currency, as well as drug offences.

Daniel Brown was handed a two-year custodial sentence for conspiracy to deliver counterfeit currency, while Mehmet Altinfincan, 27, was sentenced to five-and-a-half years in prison for conspiracy to make and deliver counterfeit currency.

Lastly, Bekir Arif, 57, was given a two-and-a-half year jail term for conspiracy to deliver counterfeit currency. He was also recalled to prison for breaching the licence period of a 23-year custodial sentence given in 1999 for supply of heroin.

According to SOCA, it is estimated that £17.5m worth of fake notes printed by the gang have been removed from circulation, while €9.3m (£8m) worth of €50 notes of the same series as ones discovered at Phillip Brown's house have also been withdrawn from across the EU. It is not known if the gang was responsible for printing the €50 notes.

During the sentencing, prosecutor Thomas Forster told the court that Phillip Brown had worked at his father John Brown’s printing firm, John Brown Printing, in Portland Road, South Norwood since he was 16 and had taken over the business in 2001 until it was liquidated in 2008.

Forster told Judge Paul Dodgson: "The brothers' experience in the printing trade provided them with the knowledge and means to forge the notes."

He added that Phillip Brown had started up PJB Printing after his father’s business collapsed and had purchased two litho presses, two Apple Mac computers in addition to equipment from John Brown Printing.

The forgery operation was uncovered by the Serious Organised Crime Agency (SOCA) and the defendants were arrested by officers in June last year after the properties from which the gang printed the money were raided.

Sentencing, Judge Dodgson said to the gang: "This was an operation that was capable of damaging the integrity of our currency and of the economy.

"The notes were of an extremely high quality. It was an operation of a professional and large scale."