LONDON (Reuters) – The head of Britain's business regulator has hit out at Ryanair, saying in a newspaper interview it may act over the way the budget Irish airline almost taunts passengers with its payment system.

John Fingleton, chief executive of the Office of Fair Trading, told the Independent newspaper the airline engaged in "puerile" and "almost childish" behaviour in the way it charges passengers for paying for flights online.

Ryanair rejected the criticism as inaccurate.

The newspaper said Ryanair advertises taxes and other fees up front but only mentions charges for paying by credit card at the end of the booking procedure to prevent customers from opting to use an alternative and free credit card to escape the fee.

Under consumer law, businesses must advertise all compulsory charges, but Ryanair offers one type of card for free.

"Ryanair has this funny game where they have found some low frequency payment mechanism and say 'Well, because you can pay with that (the charge is optional)," the newspaper quoted Fingleton as saying.

"It's almost like taunting consumers and pointing out 'Oh well, we know this is completely outside the spirit of the law, but we think it's within the narrow letter of the law'," he said.

"On some level it's quite puerile, it's almost childish. This is just playing silly games at the margins of it all and we might or might not go running after something like that."

The airline, which has clashed with the regulator before, defended itself to the newspaper.