The Competition and Markets Authority (CMA) said it had “widespread” concerns about the sites, which it has declined to name; including the role commission paid by hotels could influence their rankings and the extent to which they included all costs in the upfront price or introduced them later in the booking.
Pressure selling, involving claims about how many people were looking at the same room, how many rooms were left or how long a deal would be available, could also create a false impression of availability or rush consumers into making a decision, the CMA said.
It also raised concern about the fairness of discount claims made by the sites, such as comparisons with higher prices that were only offered for a brief time.
The CMA said it believed the sites could be breaking consumer protection law. The sites must now act to address the CMA’s concerns or face court action.