The City of London Police said there was no case to answer
The City of London Police have said there will be no formal investigation of BT over its secret trials of an ad monitoring system.
BT trialled the Phorm system - which monitors web browsing habits in order to better target ads - without the consent of users last summer.
Angry users handed over a dossier of evidence to the police following the telco's July annual general meeting.
But the police said no criminal offence has been committed.
"They said that there was no criminal intent on behalf of BT and that there was implied consent because the service was going to benefit customers," said Alex Hanff, one of the chief campaigners in the case.
Nicholas Bohm, a lawyer with thinktank Foundation for Information Policy Research, said the police response was "absurd".
"A driver who kills someone when drunk has no criminal intent. It is not a necessary ingredient of a crime," he said.
"As for the idea that consent is implied on the grounds that some people would like a service, that is not good enough at all," he added.
Stephen Mainwaring, one of the BT customers affected by the trials, said he was disappointed police have decided not to pursue the case.
"I was pretty disgusted when I found out about the trial," he told the BBC.
"I actually spotted something was going on on my PC but BT said that I must have a virus. I am pretty angry about how I was treated," he said.
He has since been offered a goodwill payment from BT and thinks other users may also have a case for compensation.
BT has declined to comment on the ruling but a spokesperson told the BBC that "BT considers claims for compensation on their individual merits."
Mr Hanff said that he will be seeking a judicial review of the police investigation.
The European Union is also currently investigating the legality of Phorm and the BT trials.
There is still no word from BT as to when the next trial of the system will begin.