(Pocket-lint) - Tesco is the first retailer to sign with Amscreen for national rollout of its digital advertising displays that can tell whether you are male or female, your age and how long you're looking at each advert.

The OptimEyes screens, which Pocket-lint told you about in July, will be installed in all 450 Tesco petrol stations up and down the UK. They utilise face detection technology and are used to collate demographic data for advertisers so they can best target future ads to specific locations.

Amscreen, a division of Lord Alan Sugar's Amshold company, claims that they cannot recognise people individually, rather take general data, such as age and sex, but privacy campaigners are still concerned.

Speaking to the Daily Telegraph, Nick Pickles of Big Brother Watch said that OptimEyes and other data collection systems could spiral out of control. He pointed out that there are already camera systems available that can recognise a shopper's face and link them to their Facebook profile to tailor special offers to their "likes" on the social network.

"People would never accept a degree of surveillance for law enforcement purposes, but these systems are solely designed to watch us for collecting marketing data," he explained.

"People would never accept the police keeping a real-time log of which shops we go in, but this technology can do just that. It is a surveillance state by the shop door."

Tesco however believes that the Amscreen system will benefit its customers.

"We're always looking to work with partners who provide innovative ways to enhance the customer shopping experience," said Peter Cattell, category director for Tesco petrol stations.

"This new dynamic screen product from Amscreen provides the perfect means for us to do this. The ability to tailor content based on time and location means it can be extremely useful and timely for our customers."

Writing by Rik Henderson.