The representative of a class action against BT, alleging that it “disproportionately overcharged” its landline customers, is seeking to overturn a court ruling that sided with the telecoms giant.

The legal action on behalf of more than 500,000 customers, by law firm Mishcon de Reya, went to trial at the Competition Appeal Tribunal (CAT) in January 2024. Consumer champion Justin Le Patourel lent his name to be the claimants’ representative.

The claim alleged that BT charged excessive prices regarding “standalone” fixed voice services, notably for older customers, and that this constituted an abuse of a dominant position.

A spokesperson for BT at the time said: “This claim relates to a technical landline pricing issue which was resolved by Ofcom in 2017. We do not accept that our pricing was anti-competitive back then, and are committed to robustly defending our position at trial.”

The proceedings were certified in October 2021, and despite BT trying to appeal that decision to the Court of Appeal, the case proceeded to a full trial at the Tribunal.

The claim was estimated to be worth £1.3bn if successful.

However, after an eight-week trial in early 2024, the Tribunal handed down its decision in December, siding with the telecoms giant. Speaking at the time, a spokesperson for the BT said the “CAT has fully dismissed the claim and found that BT Group’s conduct did not breach competition law.”

The claimants requested permission to appeal to the Tribunal but were refused in February.

The claimant’s application was denied, and the Tribunal ordered the class representative to pay 85 per cent of the defendant’s costs, which was in the region of £14m.

The representatives submitted an application to the Court of Appeal a month later.

Now the parties will attend a one-day hearing on Wednesday, as the class representative asks the court for permission to appeal the Tribunal’s decision in favour of BT.