The data being recovered includes call history, texts and contacts, and will be retained whether or not any charges are brought against suspects, the BBC reported Thursday.
Using new technology created by forensic firm Radio Tactics, cellphone content can be extracted using purpose-built terminals in police stations to produce a printout of data from the phone as well as a digital records that can be saved.
The Metropolitan Police said data extraction would only be done if there is significant suspicion the cellphone was used in connection with criminal activity.
Campaign group Privacy International has criticized the move.
"We are looking at a possible breach of human rights law," spokeswoman Emma Draper told the BBC.
"It is illegal to indefinitely retain the DNA profiles of individuals after they are acquitted or released without charge, and the communications, photos and location data contained in most people's smartphones is at least as valuable and as personal as DNA."
While the current system uses only fixed extraction terminals in police stations, portable versions of the technology exist, Draper said.
"Examining suspects' mobile phones after they are arrested is one thing, but if this technology was to be taken out onto the streets and used in stop-and-searches, that would be a significant and disturbing expansion of police powers."