London (CNN Business) Searching for a hotel room online might soon get a little more transparent, at least for UK consumers.

Major travel websites including, Agoda and Booking.com have agreed to change the way they do business after a UK investigation found some of them were deceiving users about hotel room prices and search results.

The UK Competition and Markets Authority on Wednesday announced the results of its probe, which focused on issues such as pressure selling, misleading discount claims and hidden charges.

The regulator said that some buyers were warned that other users were looking at the same hotel, giving them a "false impression" of a room's popularity. In other cases, the full cost of the room was not displayed.

While not all of the platforms engaged in each of the unfair practices, they have now agreed to follow a common set of guidelines.

The companies have pledged to display all charges including taxes and refrain from pressure selling. They will be clearer about discounts and only promote deals that are really available at that time.

The changes must be made by September 1.

Andrew Tyrie, chairman of the Competition and Markets Authority, said in a statement that the regulator will now do "whatever it can to ensure that the rest of the sector meets the same standards."

The booking industry

Expedia Group, which owns Hotels.com and ebookers, said the regulator's announcement "mischaracterizes the collaborative and good faith approach" it took in helping to establish industry standards.

"We gave commitments to the CMA on a voluntary basis and the CMA in turn closed its investigation in respect of the Expedia Group with no admission or finding of liability," a spokesperson said.

"We continue to believe our practices did not breach any consumer laws," the spokesperson added.

Trivago said it saw a "broad applicability of the guidelines to all UK online travel companies as a positive development for us and the industry," and said it would "follow them to the extent they are applicable to us."

A representative of Booking.com said it was pleased the regulator did not find an "admission of infringement."

The changes are likely to be applied selectively.

The new standards will only apply to Expedia sites registered in the United Kingdom, the company said. The other sites did not immediately respond to questions regarding whether the changes will be instituted world wide.