Kent Police has uncovered an alleged money laundering ring worth a "staggering" £5.2m in £20 notes.
The joint investigation by detectives from the Kent and Essex serious crime directorate (SCD) is considered the biggest raid of its kind in the UK.
An investigation was launched when the Bank of England knew of at least £152,000 of counterfeit cash in circulation.
Bank of England officials claim if the full extent of the alleged operation had hit the streets, "it would have had significant damage to the UK economy".
They calculated the full price of the fake notes that were kept out of circulation amounted to £5,235,000.
Chief Constable Alan Pughsley told the delivery board on June 5: "An operation commenced in January with regard to intelligence from the organised crime group counterfeiting currencies.
"Lots of work then commenced over a period including covert and overt work building an intelligence picture until May, where we believed we had identified the premises and believed there was a print run live at that time.
"It would have had significant damage to the UK economy..." Mr Pughsley
"We went to the address and found two individuals there at the time literally hands on in the middle of counterfeiting a number of £20 notes."
At least five people have been arrested as part of the alleged conspiracy to print fake notes at a business premises in Kent House Lane, Beckenham.
Phillip Brown, 52, of Ash Road, Longfield and Lucas Starczuk, 37, of Rymer Road in Croydon, have both been charged with conspiracy to produce counterfeit banknotes.
Brown and Starczuk are set to appear at Woolwich Crown Court on September 30.
A further three people have been arrested and charged.
The alleged laundering ring uncovered by Kent Police could have put £5.2million worth of fake notes in to the UK economy.
Mr Pughsley added: "This is, according to the Bank of England, the biggest ever seizure of £20 notes.
"It would have had significant damage to the UK economy.
"That is simply staggering work. Absolutely brilliant."
Details on how to check banknotes can be found at www.bankofengland.co.uk.
Anyone who receives a counterfeit note is encouraged to report it by visiting www.kent.police.uk/report or by calling 101.