The Competition and Markets Authority is launching enforcement action against a number of hotel booking sites over concerns about the way they rank and display rooms.

It is also examining whether sites are giving a false impression of room availability and pressurising customers into booking decisions, as well investigating clarity of discount claims and hidden charges.

The CMA declined to name which companies it was targeting, saying only that it had sent warning letters to a “range of sites”.

Andrea Coscelli, chief executive of the CMA, said: “Booking sites can make it so much easier to choose your holiday, but only if people are able to trust them. Holidaymakers must feel sure they’re getting the deal they expected, whether that’s securing the discount promised or receiving reliable information about availability of rooms. It’s also important that no one feels pressured by misleading statements into making a booking.

“That’s why we’re now demanding that sites think again about how they’re presenting information to their customers and make sure they’re complying with the law. Our next step is to take any necessary action – including through the courts if needed – to ensure people get a fair deal.”

UKHospitality Chief Executive Kate Nicholls said: “For consumers, the CMA’s announcement should bring some reassurance, which can not only be good news for hoteliers, too. We have been working tirelessly to highlight these practices, so are pleased to see the CMA take action.

“The CMA clearly intends to ensure that online booking sites are transparent and accurate, and that customers have complete peace of mind when booking. Extra reassurance for customers is welcome and that confidence should provide a boost for businesses.”

“The fees that OTAs charge hoteliers and B&Bs inevitably result in higher costs to the consumer - a premium of which many holidaymakers are not even aware. Consumers and accommodation providers would be better served by a wider review of the business to platform relationship, which is now overdue.

“The practices addressed here exposes yet another example of digital businesses stealing an unfair lead on honest, regulated operators whose first concern is to deliver good service to their customers.”