The City of London Police has seized second-hand clothes worth hundreds of thousands of pounds to charities in a raid on a suspected criminal gang.
Thirty officers raided a depot in Rainham, Essex, on Thursday morning, seizing £20,000 in cash, along with charity bags, computers and correspondence.
Two men were arrested on suspicion of fraud by false representation and another two were arrested shortly afterwards at properties in east London and Essex, police said. All four were later released on bail.
A police spokesman said the raid was in connection with the major investigation that earlier this year it said it was making good progress with.
The National Fraud Intelligence Bureau set up a team to analyse charity bag collection fraud in April.
The City of London Police said in a statement that charity bag fraud was costing the sector up to £50m a year.
Ian Dyson, City of London Police commander, said the raid showed how police forces and charities were sharing intelligence with the NFIB to identify and then prevent this activity.
"Investigating this type of criminality is a major priority for the City of London Police, and those who continue to offend should expect our officers to come calling some time soon," he said.
Wendy Mitchell, head of policy and public affairs at the Charity Retail Association, which has been helping the NFIB with its investigations, said it was pleased progress was being made.
The CRA has built an online tool that allows members of the public and charities to report suspicious activity to the police. Since it was set up in April, more than 100 reports of suspicious activity have been reported by this means, said Mitchell.