Confusion over airline allocated seating polices today triggered a review by the aviation regulator.

Consumers could collectively be paying almost £400 million a year for allocated seating, according to research released by the Civil Aviation Authority.

The study, covering more than 4,000 passengers who have flown as part of a group of two or more people in the last year, found that 18% were split up when they did not pay extra to sit together.

The biggest culprit was Ryanair at 35% followed by Emirates at 22%, the Civil Aviation Authority study found. Virgin Atlantic was at 18% and at 16%.

British Airways. easyJet and Thomas Cook Airlines were all at 15% while only 12% of passengers using Flybe and Tui Airways faced being split up, together with Monarch which went bust last October.

The CAA will demand more information from carriers about allocated seating practices to find out whether consumers are being treated fairly, and whether pricing policies are transparent.

The CAA research found that:

• Just over half of respondents reported that their airline informed them before they booked their flight that they would need to pay to ensure their group could sit together

• Ten per cent of respondents said that they had been informed after they booked; a further 10% said that they were never made aware by their airline that they may need to pay more to guarantee sitting together

• Although the vast majority of respondents were aware that they might not be able to sit together even if they booked as a group, almost half believed that their airline would automatically allocate them seats together

• However, two in five respondents thought that their airline would not automatically sit them together

• Around half of all passengers who sat together did not have to pay an additional charge to do so. However, 7% of respondents that ended up sitting together said that they had to change seats either at check-in or on-board to avoid being sat apart

• Different airlines may behave differently. Consumers flying with some airlines were more likely to report being separated from their group than others

• Of the group of respondents that paid extra to sit together, six in ten reported that they did so because of the risk that their airline might split their group up

• Almost half of respondents (46%) felt negatively towards the airline when they realised they would have to pay more to guarantee sitting together

The review is part of a work being carried out by the regulator this year on behalf of passengers in 2018 to include “a number reviews into airline practices”.

Besides allocated seating, also coming under the spotlight will be improving access to air travel for people with disabilities and ticketing terms and conditions.

CAA chief exeutive Andrew Haines said: “Airline seating practices are clearly causing some confusion for consumers.

“Airlines are within their rights to charge for allocated seats, but if they do so it must be done in a fair, transparent way.

“Our research shows that some consumers are paying to sit together when, in fact, they might not need to.

“It also suggests that consumers have a better chance of being sat together for free with some airlines than with others.

“The research shows that it is the uncertainty around whether their group will be split up by the airline that is driving consumers to pay for an allocated seat.

“Findings from our research show that UK consumers collectively may be paying between £160 million-£390 million per year for allocated seating.

“Of those paying, two-thirds spent between £5 and £30 per seat and a further 8% paid £30 or more. Our work will consider whether or not these charges are fair and transparent.

“As part of the review, we will be asking airlines to provide information on their policies and practices.

“We will be looking into how airlines decide where to seat passengers that have booked as part of a group and whether any airlines are pro-actively splitting up groups of passengers when, in fact, they could be sat together.

“We will not hesitate to take any necessary enforcement action should it be required at the end of the review.”

The CAA is also publishing information designed to help consumers travelling in groups to better understand their chances of sitting together without paying extra to do so.

“We are encouraging consumers to use this information and to share their experiences and concerns about seating on our dedicated webpage,” the CAA said.