Ofcom penalised O2 UK for overcharging around 140,000 subscribers which cancelled their contracts, for a period spanning eight years.

The regulator issued a £10.5 million fine after ruling O2 incorrectly billed departing customers between 2011 and 2019, stating the action was a “serious breach” of UK rules.

Ofcom enforcement and investigations director Gaucho Rasmussen said the fine was “a reminder that we will step in if we see companies failing to protect their customers”.

O2 was fined after Ofcom uncovered an error in final bills which resulted in customers being charged twice. It added the operator also failed to address problems identified in its billing process uncovered in 2011.

Ofcom began probing the issues in July 2019. It said O2 had accepted the findings of its investigation, issuing refunds to the affected customers along with a sum equal to 4 per cent of the surcharges, and changed the way it processes billing.