The ‘pay to sit together’ policy used by airlines is estimated to cost consumers between £160m to £390m per year.

Of those paying, two-thirds spent between £5 and £30 per seat and a further 8% paid £30 or more.

The regulator, the UK Civil Aviation Authority (CAA) is now concerned the risk of being separated is prompting people to pay up, yet its research revealed that in many cases, holidaymakers don’t need to fork out more to guarantee seats together.

The CAA carried out research of over 4,000 holidaymakers travelling in a group (two or more people) last year. While many were aware all members of the party may not be able to sit together, almost half believed the airline would automatically allocate them seats together. Only two in five thought the airline would not automatically seat them together.

Around half of all passengers who sat together didn’t have to pay extra, though 7% said they asked to change seats at check-in or on-board to avoid being separated.

The CAA research also revealed just one in five (18%) who didn’t pay extra to sit together were separated from the rest of their group on the flight.

Of those who did pay extra to guarantee their seats, six in 10 reported they coughed up the cash for fear they would be split up.

The way travellers were informed whether they would need to pay to sit together on the flight also varied by the airline.

The CAA found just over half said their airline informed them before booking a flight that they would need to pay to ensure the group could sit together.

One in 10 said there were informed after they booked their flight while a further 10% said they weren’t told by the airline that they may need to pay more to guarantee seats together.

The CAA research also revealed holidaymakers flying with some airlines were more likely to report being separated from other members of their party than others.

Overall, the allocated seating policy made people feel negatively towards the airline (46%) when they were told they would need to pay more to sit together.

The table below shows the chances of being separated if not paying extra to guarantee seats by airline:

The CAA is now seeking more information from airlines about their allocated seating practices to check whether holidaymakers are being treated fairly, and whether these policies are transparent.

Andrew Haines, chief executive of the CAA, 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.”