While the US has seen a vibrant and relatively transparent debate around so-called IMSI catchers—devices that can indiscriminately sweep up texts, calls and other mobile phone data in a given area—the UK government has remained consistently tight-lipped about its use of the tools.
But, slowly, more information is trickling out. According to financial documents uncovered by Motherboard, another UK police force has allocated funds for buying IMSI catchers. One of the documents also implies that the force shares this type of surveillance technology, meaning that the total number of agencies across the country that can use IMSI catchers may be greater than currently understood.
"These documents suggest that a far wider group of police forces are making use of the technologies and it is no longer just the counter-terrorism units in the larger forces," Eric King, a visiting lecturer in surveillance law at Queen Mary University of London, told Motherboard in an email.
Essex Police has allocated a total of £145,000 to "CCDC Platform Equipment", according to a budget spreadsheet. Some £122,500 of that cash was to be spent across 2016 and 2017, while the remaining £22,500 is apparently due to be used in 2018 or 2019, judging by the document. As a Bristol Cable investigation found, CCDC stands for covert communications data capture, and experts strongly believes it refers to IMSI catchers.
IMSI catchers, otherwise known as cell-site simulators or sometimes Stingrays after a particularly popular brand, masquerade as cellphone towers. Once phones in a potentially wide area connect to the device, it grabs a SIM card's unique identifying code—an IMSI number. Some models of IMSI catcher can also intercept phone calls and text messages.
Other documents previously detailed links between CCDC and London's Metropolitan Police, West Mercia, Warwickshire, West Midlands, Staffordshire, Avon and Somerset, and South Yorkshire forces.
Notably, the spreadsheet marks this Essex CCDC expenditure as "joint with Kent," and Motherboard also found a second document, this time from Kent Police, mentioning covert communications data capture. (That file has seemingly been removed from the Kent police website; multiple forces have tried to scrub evidence of CCDC purchases).
The expenditure on CCDC also includes the acronym "SCD," which appears to refer to the Serious Crime Directorate, a joint command between Kent and Essex Police. The SCD has conducted investigations into lorry thefts, murder, human trafficking, and more.
It is not totally clear what specific sorts of crime Essex and Kent Police would use CCDC to combat though, or whether they would obtain court approval beforehand. The forces have published joint policies around other surveillance technology, such as Automatic Number Plate Recognition (ANPR), but not for CCDC.
A spokesperson for Essex Police told Motherboard in a statement that "the Kent and Essex Serious Crime Directorate uses a range of techniques to prevent and detect crime and protect the public from harm and it does so within the parameters of all relevant legislation. However, it is our policy to neither confirm nor deny the acquisition or use of any specific surveillance methods, or technology used."
This sharing of surveillance technology between UK law enforcement bodies appears to happen frequently. Motherboard previously obtained a Memorandum of Understanding between City of London Police and the Competition and Markets Authority (CMA), which investigates price-fixing cartels. That document showed that CMA would borrow spying tech from the police, and promise to keep any sensitive details secret.
"The police should stop pretending IMSI catchers don't exist and instead explain the warranty process they believe authorises their use and request oversight bodies expressly report on police use of them. That's the appropriate way to act in the public interest and I hope the police make changes in this area to be more transparent and accountable," King said.
Update: After the publication of this article, Essex Police provided a statement. This article has been updated with that statement.
Subscribe to Science Solved It, Motherboard's new show about the greatest mysteries that were solved by science.