A UK shopping centre is one of the first to track where shoppers go and what shops they visit, through their phones: Channel 4 News paid a visit to find out what it is doing with the data.

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Shoppers across the UK are being tracked and targeted by new technology which hoovers up data from their mobile phones without their knowledge.

At least a dozen shopping centres and hundreds of shops have installed wi-fi tracking to monitor behaviour - not just of visitors, but even passers-by who do not go inside.

Channel 4 News was given exclusive access to the Kingsgate shopping centre in Huddersfield, which is one of the first to use the new technology.

Visitors to the centre who have their phone's wi-fi turned on are instantly picked by the system, which logs the unique ID of the phone. It enables the centre to track whether a shopper's phone has visited before, how long it stays, and how far into the centre it goes. In future the system could be used to plot shoppers' locations to within a few metres.

You can actually see how many people are looking at a display and thinking I want to go and have a look at that. Gavin Wheeldon

"What you're able to do is see how people move around," said Gavin Wheeldon from Purple Wifi, the company which installed the system. "Every wi-fi device is merrily pinging away in the background looking for a wifi signal.

"What we can tell how often it comes, how often it stays how engaged it is, how far it comes into the venue. For somewhere like this they've never had this kind of data."

But the system also tracks people who don't come inside the centre, because its wifi detectors cover the pavement outside.

"You can actually see how many people are looking at a display and thinking I want to go and have a look at that," said Mr Wheeldon.

Police access

There are no signs on display to warn people about the system. Purple Wifi insists it is not collecting personally identifiable information. “We don't know who you are, we don't know anything about you,” said Mr Wheeldon. "All we've got is that tiny bit of information."

But the company confirmed that, with a warrant, police can access its store of phone IDs to find out where and when a phone appeared.

If visitors want to use the centre's free wifi, they are asked to hand over even more information. To sign in they're encouraged to use social media services such as Facebook, and agree to giving Purple Wifi access to elements of their Facebook account, including their email address and likes. This information can then be used to target bespoke emails.

But privacy campaigners argue it is easy to link a phone's ID with other information about its owner. "We should look at these unique IDs to phones similar to fingerprints," said Mike Rispoli of Privacy International.

We should look at these unique IDs to phones similar to fingerprints. Mike Rispoli

"Just looking at them you may not know that much about it. But it's trivial to connect that to other personal info about yourself, so shops and other authorities can connect your phone to your real world identity."

If visitors want to use the centre’s free wifi, they are asked to hand over information. To sign in they’re encouraged to use social media services such as Facebook, and agree to giving Purple wifi access to elements of their Facebook account, including their email address and likes. This information can then be used to target bespoke emails.

"What we can do is target our marketing more specifically," said centre manager Jonathan Hardy. "What it will enable us to do in future is to say to loyal customers, to specific genders or age groups…. we have these offers on at this specific shop that will appeal to you."

Using the free wifi also means shoppers "like" the Kingsgate's Facebook page, meaning its Facebook posts will appear on shoppers' friends' newsfeeds.

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