Passengers who pay extra to sit together when they fly are wasting their money in the vast majority of cases, a new Which? Travel investigation has found.

The consumer organisation analysed the experiences of 3,357 economy passengers and found that, out of those who refused to pay the extra fee to select a seat, 86 per cent ended up seated together anyway.

That figure rises to 90 per cent if Ryanair is excluded from the list of airlines.

The Irish budget carrier had by far the lowest proportion of passengers seated together if they had not paid extra for allocated seating, at just under half (46 per cent).

The airline admits that it does not try to keep groups together, but has always denied actively splitting them up in order to boost its profits.

Which? Travel also asked the ten most popular airlines that operate paid-for seating options whether or not they seat families, couples and groups together, all of them confirmed that they did with the exception of Ryanair and Wizz Air.

BA said: “We recommend that you reserve your seat as early as possible to avoid sitting separately from your family or friends’ during the booking process.”

But 91 per cent of the British Airways customers who didn’t purchase allocated seating still got to sit together regardless.

Families with children should be protected by the Civil Aviation Authority guidelines, which state that airlines should ‘aim to sit parents close to children’ and that parents should not have to pay to avoid being seated away from their child.

But airlines are not currently obliged to follow this advice.

Which? has heard from parents who have been separated from children as young as four on flights, and there is a lack of consistency in how airlines handle the issue.

Some airlines (including BA, Thomas Cook and Tui) state that children under 12 will always be seated with at least one adult.

But Ryanair ignores these guidelines and forces families to pay to sit together: it’s compulsory for at least one adult in the group to select a paid-for seat.

They can then reserve seats (for free) for up to four children.

When the CAA surveyed recent flyers last year, it found nearly one in five (18 per cent) had paid extra for seat reservations because they were travelling with children.

However, Ryanair told Which? that it “fully complies with all EU safety regulations” and Wizz Air said, “the safety of our passengers is always our number one priority”.

Rory Boland, Which? travel editor, said: “Unless you are flying with Ryanair or Wizz Air or fancy a little extra legroom, it’s not worth paying more to choose your seat, as you’ll be seated next to your travelling companions anyway.

“It’s worrying to hear that parents are being separated from young children.

“It’s reprehensible for any airline to make money by splitting up families and we would encourage the regulator to examine such cases closely to ensure the guidelines are working.”