Ryanair

Ryanair says its choice of Electron as the only fee-free card is down to a deal to boost the card's popularity. "We're working with Visa to promote the Visa Electron card, and we do so by encouraging all passengers booking on Ryanair to use it, as this enables passengers to avoid any optional debit- or credit-card handling fees," a spokesman for the budget airline says.

However, its website says that, as a special offer to Visa Electron card holders, no handling fee will be charged for "a limited period only". Flights bought fee-free with Visa Electron cards began in 2004. The Electron promotion also allows the airline to continue to advertise its flight deals at rock-bottom prices despite much higher final costs for most customers.

Ryanair's new £4 fee brings debit cards into line with credit card payments, and joins the growing list of Ryanair charges to watch out for, including checked baggage, airport check-in and excess baggage fees.

Giles Howard, a 42-year-old businessman from St Albans, Herts, says he was let down by the debit-card charge that he says was not up-front or made clear until his flight confirmation.

Enticed by an advert for a £2 Ryanair flight sent to him in an email, and having booked plenty of budget seats before, he was savvy enough to know he would have to book carefully to avoid add-ons. He painstakingly picked four £2 return flights to France last month.

Delighted at his £8 bargain holiday, he was then gobsmacked to receive a flight confirmation email telling him he owed £40. "I knew I was going to pay with a debit card - usually the cheapest way - and I did check the running total after each selection to make sure that the total was as advertised," he says. "But you certainly do not expect your method of payment to make a five-fold increase to the price."

Ryanair disputes this and says that the terms and conditions of handling fees are made very clear. Of course, Howard would not have had to fork out £40 if he had paid with Visa Electron - a detail he says he discovered too late.

"Even though it was still a cheap deal, I feel the airline relies on not many people having Electron cards to be able to advertise those flights at £2," Howard says.

In response, the Ryanair spokesman says that "almost 20% of our customers book with Visa Electron", and stresses that Howard benefited from its lowest fares.

The Office of Fair Trading says it believes any decision over whether to charge for making payments by credit or debit card is one for the trading company. "However, we are of the view that fixed non-optional charges should be included in all prices so that consumers are not misled," a spokesman says.