The claim alleges that Experian sold people’s data to advertisers for targeted marketing without their permission and that this was a significant breach of the General Data Protection Regulations (GDPR).

The case was launched by law firm Harcus Parker in the High Court on 26 February. The firm is acting for a representative claimant – Liz Williams from Gillingham in Dorset. She filed a writ for £750 in damages.

The case has been filed as what’s known as ‘representative action’. This means that while Harcus Parker is launching the case on behalf of one person, a win would mean millions of people could claim compensation.

About 46 million people in England and Wales will have a credit history with Experian. If the case is successful and they all claim £750, the total claim could reach £34.5bn.

The court case comes after data regulator, the Information Commissioner’s Office (ICO), took enforcement action against Experian last year.

The ICO found Experian was “trading, enriching and enhancing people’s personal data without their knowledge”.

It told Experian to tell people that it holds their personal data and to make clear how it is using or intends to use it for marketing purposes by July 2021.

But Experian disagrees with the ICO’s decision and is in the process of appealing.

It also disagrees that there is any basis for the Harcus Parker legal claim.

A spokesperson for Experian said: “For more than 30 years, our offline marketing-services business – which is separate from our credit-reporting business – has supported thousands of small companies, charities and public bodies, using publicly available data such as the census and the edited electoral roll. It does not use any cookies to track or monitor internet behaviour and does not collect data on actual customer purchases.”