The investigation was conducted by the UK-based Sky News, and its findings were released on Wednesday.
The poles, which were found in London, have on them tools known in the communications industry as International Mobile Subscriber Identity, also known as Stingrays.
It was the first time such espionage tools were detected in the country.
According to the investigation, the fake communication posts are actually intercepting phone calls and collecting all their data.
Authorities, however, have not revealed who is controlling the masts and for what purpose.
In the past, the Scotland Yard, the territorial police force responsible for policing most of London, reportedly bought some of the posts on which the spying devices were found.
The transactions were said to be conducted by the Scotland Yard in 2009, leaving many to suspect that the police force is behind the spying on UK citizens.
Commissioner Bernard Hogan-Howe, from Scotland Yard, told British media: “We’re not going to talk about it, because the only people who benefit are the other side, and I see no reason in giving away that sort of thing.”
The UK government is notorious for carrying out espionage against its citizens, past reports have showed.
Earlier this year, British lawmakers for the first time acknowledged that the country’s spy agencies are snooping on private communication data in bulk.
A report by the British parliament’s Intelligence and Security Committee revealed in March that British government spies were reading thousands of private communications every day. But it said the interception does not count as blanket surveillance.
Britain’s spy agency, the Government Communications Headquarters (GCHQ) and its American counterpart, the National Security Agency (NSA), were at the center of a scandal following leaks from former US intelligence contractor Edward Snowden. The two agencies are accused of eavesdropping on not only some of the top world leaders but even ordinary citizens across the globe.
According to the revelations by Snowden, the GCHQ received private communications intercepted by the NSA through its “mass surveillance” programs, known as Prism and Upstream.