EMPLOYEES at a mobile phone company are facing prosecution after it was revealed millions of customers’ contract details were sold on to third parties.

T-Mobile, which has its head office in Hatfield Business Park, confirmed yesterday evening it had been the subject of an investigation by the Information Commissioner’s Office (ICO).

The company, the UK’s fourth largest mobile phone operator, alerted the ICO after becoming suspicious of customer data being passed on to rival companies.

The investigation found that T-Mobile staff had been selling customers’ contract details to rival operators, who would then cold-call the customers when their deals were close to expiring.

A T-Mobile customer contacted the Welwyn Hatfield Times this morning, saying he believed he was a victim of the breach.

“I have received four or five calls trying to get me to change my tariff or get a new handset as I am currently at the end of my contract,” he said.

“When I have asked these other operators who they are, they have always said they work on behalf of T-Mobile, but are different companies. They offer all kinds of incentives and talk really quickly to try and bamboozle you, and when you dismiss their offers they tend to get very irritated- it’s quite an aggressive sales technique that these companies use.”

A T-Mobile spokesman said: “T-Mobile takes the protection of customer information seriously. When it became apparent that contract renewal information was being passed on by an employee to third parties without our knowledge, we alerted the ICO.

“Working together, we identified the source of the breach which led to the ICO conducting an extensive investigation which we believe will lead to a prosecution.”

The spokesman would not confirm whether the staff in question worked at the Hatfield head office because, before the breach was made public, “we had been asked to keep all information on this case strictly confidential so as to avoid prejudice to the investigation and prosecution.”

Information Commissioner Christopher Graham has said those responsible will be prosecuted, and called for custodial sentences to be introduced for breaches of the Data Protection Act, which currently only carries a maximum �5,000 fine.