More than £4m worth of fake one pound coins have been seized by detectives.
The haul is thought to be the biggest ever in the UK and follows raids on properties around London.
The Metropolitan Police received information from a member of the public that led to raids at addresses in Enfield, Essex and Hertfordshire.
The vast majority of the coins were found in a 40ft freight container in Waltham Abbey, Essex.
Detective Inspector Bruce South said: "This seizure is a significant blow to the network behind it - individuals clearly intent on undermining the UK monetary system by producing counterfeit currency on an industrial scale.
"It is yet another example of the work this team is carrying out on a daily basis to tackle organised criminal networks."
Three men have been arrested and are being questioned on suspicion of making counterfeit money, money laundering and fraud.
The suspects - aged 52, 43 and 27 - are being held at a north London police station.