The competition watchdog is investigating if car hire websites are punishing customers with unexpected fees.

The Competition and Markets Authority (CMA) has not named the two comparison sites. However, they fear they may be breaking consumer law by not accurately telling drivers the full price of their car hire before they book. Customers only learnthe true cost when they pick up the vehicle. Many feel they are left with no choice but to accept the fees.

The CMA said it had not decided whether the two comparison sites had broken the rules. It will now consider their responses to its concerns. They could face legal action if they do not make any required improvements.

The news comes as car hire companies ramp up costs for the half-term holiday. For example, travellers will pay an average of £190 for a week’s car hire in Cyprus, compared with just £110 if they went away at a different time. 

The CMA has issued letters to 40 other websites that offer car hire, instructing them to keep up standards and, where necessary make improvements.

In particular, it wants the sites to: show all extra charges initially; clearly display fuel pricing policies; and give warnings about high additional costs.

The CMA’s announcement builds on its investigation with the European Commission into the big five rental firms — Avis Budget, Enterprise, Europcar, Hertz and Sixt. It said this had resulted in savings of £100m for UK consumers.