A military-grade encrypted communication system used by organised criminals trading in drugs and guns has been hacked by law enforcement in one of the biggest operations of its kind.

Thousands of officers from the National Crime Agency, regional crime squads and every police force in the UK have been involved in a massive international sting that was launched in April.

More than 700 people have been arrested so far, including police officers and law enforcement officials, and drugs worth £80 million, 77 guns and more than £54 million in cash has been seized.

After four years of work by international teams, French investigators managed to access Encrochat, an encrypted platform used by 60,000 people worldwide, including around 10,000 in the UK, for what law enforcement agencies claim were purely criminal purposes.

The company, which charged £1,500 for a device on a six-month contract, sent out a warning to users in early June to say that its servers had been hacked by a government entity.

This left investigators with a race against time to make the most of the wealth of information available on the platform, targeting “Mr and Mrs Bigs” before they could cover their tracks.

International investigators were also going after the team who ran Encrochat, who they said led “luxury lifestyles”, although the technology itself is not illegal.

National Crime Agency (NCA) director of investigations Nikki Holland said the breach – described by one official as like breaking the Enigma code – was like “having an inside person in every top organised crime group in the country”.

She said: “This is the biggest and the most significant law enforcement operation of its kind in the UK and it is previously unmatched in terms of its scale.

“We have dismantled well-established organised crime groups and have already secured evidence to prosecute a significant number of known criminals that have previously remained beyond our reach.”

So far, officers in the UK have arrested 746 suspects and seized more than £54 million in cash, as well as 55 sports cars and 73 luxury watches.

They have taken control of more than two tonnes of class A and B drugs, as well as 28 million street valium pills – a drug that has caused a number of deaths in Scotland.

A total of 77 guns, including sub machine guns, as well as 1,800 rounds of ammunition and four grenades have also been seized.

The NCA said UK law enforcement had dealt with more than 200 threats to life and had “undoubtedly” prevented murders between rival gangs.

These included chilling plots to remove limbs, stage acid attacks and carry out shootings as part of turf wars.

Law enforcement have been aware of Encrochat for some years. Drug dealers Andrew Venna and Matthew Cornwall, who operated in Gloucester and Stroud, used the devices before they were jailed in May 2019; as did Mark Fellows and Steven Boyle, who were jailed for life last year for the 2015 gangland killings of John Kinsella and Paul Massey in Liverpool.

After the platform was accessed, investigators were able to monitor thousands of Encrochat handsets and analyse millions of messages to get information on drug dealing, the sale of illegal guns and money laundering.

Several organised crime gangs active in the UK, a number in double figures, have been dismantled.

NCA deputy director Matt Horne said: “This is very much about the organised crime gangs that are operating on street corners, on estates and across communities across the entire UK. Trafficking drugs and using serious violence and use of firearms.

“It hits right at the heart of the most dangerous organised criminals that are actually on the streets of the UK, that we need to target, and cause real problems for our communities.

“I assess this is the largest-ever disruptive impact against organised crime gangs operating at a high level involved in drugs importation, in drug trafficking, firearms importation/trafficking, and money laundering that impacts on the UK.”