Mobile operator EE has defended plans to sell its data, after a newspaper reported personal information was being offered to the Metropolitan Police.
Research company Ipsos Mori has an exclusive deal to sell on EE's data, and has held talks with the force, according to the Sunday Times.
EE told the BBC the article was "misleading to say the least".
The company said Ipsos Mori had access only to anonymised data grouped in samples of 50 people or more.
"We would never breach the trust our customers place in us and we always act to comply fully with the Data Protection Act," a statement from EE said.
"The information is anonymised and aggregated, and cannot be used to identify the personal information of individual customers."
The newspaper's report said information about 27 million of EE's customers was on offer - including their gender, age, postcode, the websites they visited, the time of day they sent texts and their location when making calls.
The Met Police confirmed to the BBC that they had held an "initial meeting" with Ipsos Mori to discuss how the data could be used to tackle crime, but added it "has made no offer to purchase data from Ipsos Mori nor has any intention of doing so".
The force would not comment on whether it had made similar enquiries with other mobile operators.
In response to the story, Ipsos Mori - which is yet to fully finalise the terms of the deal with EE - told the BBC the data set was "not about individuals - it's about behaviour".
On its website, the research company outlined what powers it had:
- We can see the volume of people who have visited a website domain, but we cannot see the detail of individual visits, nor what information is entered on that domain
- We only ever report on aggregated groups of 50 or more customers
- Ipsos Mori only receives anonymised data without any personally identifiable information on an individual customer
- We do not have access to any names, personal address information, nor postcodes or phone numbers
'Movement of crowds'
Monetisation of mobile-data intelligence is a major new revenue source for operators.
Clues about a user's location, and what they are interested in, are a potential goldmine for retailers looking to offer targeted advertising.
Other networks such as Vodafone and O2 also offer businesses the chance to capitalise on the personal information it holds on its customers.
"Aggregated, anonymised data based on analytics such as footfall and outdoor media tracking can enable an organisation to make informed decisions," said Vodafone in a recent press release about services it offers.
Likewise, O2 offers "analytical insights" to retailers through parent company Telefonica, whose digital insights team - set up last year - promises "a digital headcount to help them understand the movement of crowds".
"Retailers are quite good at measuring footfall inside their stores," the company said.
"But this data will tell them where people go once they are outside, as well as their age and gender."
Such schemes have attracted the concern of privacy rights campaigners - particularly at a time when debate over what access the government should have to private data is under scrutiny.
Last week, proposals for the Communications Data Bill - referred to by some as the Snoopers' Charter - was left out of the Queen's Speech.
The bill called for greater powers to investigate crime in cyberspace - but was opposed by the Lib Dems who said the measures went too far.
On news the Met Police was in contact with Ipsos Mori about mobile data, one privacy group told the BBC it was "alarmed".
"There is no point in the government announcing that they don't want a Snoopers' Charter only to get a privatised one by the back door," said Loz Kaye from the Pirate Party UK.
"Companies must start to realise that it is against their interests to treat their customers this way. Otherwise we just end up being commodities in a 21st Century data gold rush."
Follow Dave Lee on Twitter @DaveLeeBBC