EXPEDIA and Trivago are among six online hotel booking sites that have agreed to a raft of changes to end misleading sales tactics and hidden charges after a probe by the competition watchdog.

Booking.com, Agoda, Hotels.com and Ebookers were also investigated by the Competition and Markets Authority (CMA) after it raised 'serious concerns' over tactics used in the sector.

The CMA said the sites have voluntarily committed to the measures, including changes to make search results clearer, to end pressure selling, make discount claims more transparent and display all compulsory charges.

The CMA said it will 'do whatever it can' to bring the rest of the online hotel booking sector up to the same standard.

Action was taken last year after concerns practices such as giving a false impression of a room’s popularity or not displaying the full cost of a room upfront could mislead people, stop them finding the best deal and potentially break consumer protection law.

All companies under investigation by the CMA have co-operated with its work and voluntarily agreed to the following:

Search results: making it clearer how hotels are ranked after a customer has entered their search requirements, for example telling people when search results have been affected by the amount of commission a hotel pays the site.

Pressure selling: not giving a false impression of the availability or popularity of a hotel or rushing customers into making a booking decision based on incomplete information.

For example, when highlighting that other customers are looking at the same hotel as you, making it clear they may be searching for different dates.

The CMA also saw examples of some sites strategically placing sold out hotels within search results to put pressure on people to book more quickly. Sites have now committed not to do this.

Discount claims: being clearer about discounts and only promoting deals that are actually available at that time.

Examples of misleading discount claims may include comparisons with a higher price that was not relevant to the customer’s search criteria.

For example, some sites were comparing a higher weekend room rate with a weekday rate or comparing the price of a luxury suite with a standard room.

Hidden charges: displaying all compulsory charges such as taxes, booking or resort fees in the headline price.

Sites can still break that price down, but the total amount the customer has to pay should always be shown upfront.

Andrew Tyrie, chairman of the CMA, said: "The CMA has taken enforcement action to bring to an end misleading sales tactics, hidden charges and other practices in the online hotel booking market.

"These have been wholly unacceptable."

The CMA stressed that not all of the six sites were guilty of using the tactics but have still committed to the changes.

They must make the changes by September 1 and the CMA will monitor their compliance.

The watchdog will write to hotel booking sites across the sector - including travel agents, metasearch engines and hotel chains - to explain how they must comply with consumer protection law.