Key evidence that helped convict two British men last week for terrorist offences was reportedly obtained from a locked phone using a simple but highly effective ruse.

According to CNN, which cited a source close to the investigation, undercover police officers visited Junead Khan, 25, of Luton posing as company managers and asked to check his driver and work records.

"When they disputed where he was on a particular day, he got out his iPhone and showed them the record of his work. The undercover officers asked to see his iPhone and Khan handed it over," CNN reported. At that point they apparently arrested Khan and changed the password settings on the iPhone to prevent it from becoming locked.

Dean Haydon, head of the Metropolitan Police's counter terrorism command, told CNN: "Via that phone we knew that they'd been in contact with Daesh fighters in Syria via text message, via e-mails but also using social media applications but also there was a vast amount of extremist and terrorist material on there in relation to how to make a bomb, for instance, but also material that related to atrocities overseas."

The Met indicated that encryption was not a problem when obtaining further valuable digital evidence in the successful conviction of Khan and his uncle for "engaging in conduct in preparation of terrorist acts." Scotland Yard said: "Digital forensic analysts sifted through around 64,000 files from Junead Khan's three computers, recovering deleted documents. These included bomb making guides and terrorist propaganda."

According to the CNN report, Khan was planning to stage a car crash near a US or RAF military base and then attack a US airman with a knife. "He'd also researched and planned on how to make a pressure cooker bomb," Haydon told CNN. "We think that that bomb was going to be detonated if he was compromised by police either before or during the actual attack."

UK police were not only aware of Kahn's activities, but they actively tried four times to dissuade him from engaging with other known terrorists, the Met said.

This latest terrorism case appears to provide a good demonstration of how encryption can be circumvented using old-fashioned but highly-effective policing techniques. Arguably, the easiest way to deal with a secure system is often to concentrate efforts on what is generally the weakest link—the human element.

Kahn and his uncle, Shazib Khan, 23, also of Luton, were found guilty of engaging in conduct in preparation of terrorist acts following a six-week long trial at Kingston Crown Court. The two men have been remanded in custody until they are sentenced on May 13.