The report examined the websites of 20 of the UK's online travel agents and airline carriers. Each website studied was evaluated against a set of 20 best practice guidelines and assigned a score of zero to five for each guideline, using a system that was developed by Webcredible specifically for travel websites.
Travel agents achieved just 55% usability and airline carriers only 48%. In an industry in which margins are slim, and self-service could give an operator a distinct business advantage, this could be an expensive failing, suggested the report.
The standard varied enormously, although profitability did not seem linked to usability. Although Opodo, British Airways, and Travelbag scored more than 60% on their ability to offer customer usability functions, Ryan Air and Monarch airlines - at the other end of the scale - achieved around 40%.
Ryan Air was criticised for the lack of transparency of its pricing.
Meanwhile, many of the top internet brands performed very poorly, only scoring about 50% on the usability scale. On average travel agents - led by online specialists such as Opodo and Travelbag - scored 55% and the airline carriers achieved 48%.
Ismail Ismail, director at Webcredible, said that transparency of pricing is important to a company's success, despite the fact that it has not affected Ryan Air adversely. "Users need clear and accurate pricing displayed all their way through their web site journey. It is not acceptable to add hidden charges at the very end of a transaction process - this is something that a number of airline carriers are guilty of."
Ismail said there was a general failure to embrace Web 2.0 technologies, with few sites able to provide their users with such rudimentary sharing tool features as options to "e-mail a friend".
"It is surprising that many of the sites tested have not embraced the spirit of Web 2.0, considering its growth in recent years. Booking a holiday is often a social experience and the ability to interact and share the booking process with friends and family is essential," he said.
With the European air travel industry worth around £38.6bn, Ismail warned that top travel sites must use every IT advantage available in a highly competitive market.
"Increasing the usability of a travel website will enhance the success users have in finding and booking flights - it is as simple as that. Better usability will also lead to a rise in loyalty and return site visitors, and an improvement in the perception of the online and offline brand," he said.