The action was linked to Operation Venetic, a national effort to tackle the supply of illegal drugs which led to the cracking of a secret phone system used by organised criminals.
London's Metropolitan Police used EncroChat data to launch what it called its most significant operation against organized crime, saying in a statement that it had arrested "some of London's longest-standing and most risky criminals" and seized more than 13 million pounds in cash.
EncroChat had 60,000 users worldwide with the operators behind the service selling the special customised Android phones for €1,000 each with a six-month contract costing €1,500, said the European police body Europol.
The multiyear investigation resulted in arrests in France, the Netherlands, U.K., Sweden and Norway, Europol announced Thursday.
The NCA also reported that in excess of two tonnes of drugs, several dozen guns and £54m ($67.34m) in suspect cash were seized as a result of the communications system being penetrated.
"Organized crime groups have used encrypted communications to enable their offending". Because of the trusted nature of the app, people would openly discuss drug deals, murders, and other crimes, making them sitting ducks for law enforcement.
Police said it targeted organised crime groups using encrypted technology "in a bid to evade law enforcement".
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Officers from Hertfordshire Constabulary's Serious and Organised Crime Command (SOCC) executed warrants under the force's own Operation Relentless, which was launched previous year, targeting people with links to organised crime and drug supply networks.
The UK's National Police Chiefs' Council lead for serious organized crime, Chief Constable Steve Jupp, said the "unique operation" was focused on those believed to be at the highest level of organized crime.
However, the encrypted communication network was not so secure, as French and Dutch police successfully hacked into the network and analyzed millions of messages and hundreds of thousands of images in real-time, "over the shoulder of the unsuspecting senders".
He said that over the past couple of months PSNI officers have worked with the NCA and HM Revenue and Customs in reviewing the material seized and assessing what criminal offences have been committed.
Drug dealers Andrew Venna and Matthew Cornwall, who operated in Stroud and Gloucester, used Encro Chat before they were jailed last May.
"By dismantling these groups, we have saved countless lives and protected communities across the United Kingdom", he added.
"It is the broadest and most significant co-ordinated piece of activity into serious organised crime meant to cause significant damage to organised crime groups".
This operation demonstrates that criminals will not get away with using encrypted devices to plot vile crimes under the radar.