In a report published by Sky News, evidence is shown that fake cell towers are being used in London, which have the ability to eavesdrop on calls and collect additional communications data. Named IMSI catchers, or by the brand name Stingray, the tower -- which can actually be the size of a briefcase, and equally as portable -- fools phones into connecting with them, and are apparently used by the police and governments to monitor crime.

However, according to privacy experts, it's very difficult to target specific groups or individuals using an IMSI catcher -- meaning anyone with an active phone could be caught out by the tower, and inadvertently have their communications monitored. The report represents the first time evidence has been shown of an IMSI catcher's use in the UK.

Related: Is your smartphone being tracked? We asked an expert

To gather evidence, Sky News used a special smartphone called the CryptoPhone, a modified Samsung Galaxy S3 that provides an array of security and protection features. Using the phone for three weeks, Sky News found the device connected to Stingrays more than 20 times. It has made the logs available for the public to see, and for other experts to analyze. Cryptophone's CEO backed up the claims, saying, "The abnormal events encountered can clearly be categorized as strong indicators for the presence of IMSI catchers in multiple locations."

Law enforcement's keeping quiet

The story comes at a time when concern over privacy, security, and government-backed eavesdropping is at a high point. However, despite Sky News findings, the UK's police commissioner had little to say on the subject when asked for comment. He said the only people who would benefit from knowing details are the criminals, and he "saw no reason in giving away that sort of thing."

Also avoiding the subject was director-general of the National Crime Agency in the UK, who said opening up the debate would "defeat the purpose of having the tactics in the first place," and added that, "some of what we need to do is intrusive, it is uncomfortable." Ultimately, Sky News didn't receive a clear confirmation or denial regarding the use of IMSI catchers in the UK.

Documented use in the U.S.

IMSI catchers aren't new technology, and have been around for several years. Their use is already relatively well documented in the U.S., and one of the devices was at the center of a major trial in 2011, when it was allegedly used to apprehend Daniel Rigmaiden, AKA the Hacker. At the time, the FBI also stated that revealing too much about the device could "compromise future use," and mean it could be, "defeated or avoided or detected."

While Sky News went to the trouble of obtaining a $3,500 CryptoPhone for its investigation, if you're at all concerned about ISMI catchers -- and making law enforcement's concerns about detection of such devices rather moot -- SnoopSnitch says it's clever enough to warn you about the presence of fake base stations, and it's available as an app for your Android phone, for free, through Google Play right now.