What encryption did Encrochat use, and how was it broken?

On 2nd July, the UK’s national news outlets broke the story of an "unprecedented" 4-year-long, Europe-wide investigation that, in the UK, resulted in the arrest of 746 criminals, including many high-profile "kingpins" of the criminal underworld as well as corrupt police officers. According to The Mirror:

NCA Director of Investigations Nikki Holland, said: “This is the broadest and deepest ever UK operation into serious organised crime. Together we’ve protected the public by arresting middle-tier criminals and the kingpins, the so-called iconic untouchables who have evaded law enforcement for years, and now we have the evidence to prosecute them.”

If these phones were employing a form of encryption, then it stands to reason that the French police and the UK’s National Crime Agency must have been able to break it in some way. Is there any further information on what encryption EncroChat phones were using, and how exactly it was broken?