Passengers due to travel with Ryanair tomorrow are being urged to check in online early to avoid airport chaos — and possible surcharges.

Essential “upgrade maintenance” work will close its website for 11 hours from 6pm today until 5am tomorrow.

Those flying with the no-frills airline tomorrow should therefore check-in online by 6pm today and bring their boarding pass to the airport.

Travellers who arrive without a boarding pass could be charged a £40 ‘boarding card re-issue fee’ — introduced by Ryanair last month.

The penalty will not apply to passengers who booked flights on or before May 21, provided they have already paid for Ryanair’s airport check-in service.

Ryanair’s Stephen McNamara said that all passengers had been emailed about its imminent website closure five days ago.

“We would remind passengers who are due to travel on Thursday that our web check-in facility will not be available from 6pm on Wednesday [today] until 5am on Thursday,” he said.

“To avoid any chaos at the |airport, we wish to again urge web check-in passengers that |they must check-in and print |off their boarding card on www.ryanair.com before 6pm on Wednesday.”

Last month, the company announced it is imposing a £10 per return flight fee for online check-in ahead of plans to phase out its airport check-in desks.

Despite publicity, many passengers were caught out when the £40 ‘boarding card re-issue fee’ came into place.

Referring to potential problems connected with this week’s website shutdown, Mr McNamara moved to reassure Ryanair customers.

“Customer service representatives will be able to assist passengers which have any difficulty checking in as a result of the closure,” he said. “Passengers are also unlikely to be faced with the €40 charge, but Ryanair encourages all passengers to check in as normal beforehand.”

Mr McNamara also apologised for any inconvenience caused.

Meanwhile, it emerged that more than 50 airlines had reformed online booking sites — or intended to do so soon — after the European Commission introduced the first EU-wide enforcement action, threatening to “name and shame” certain carriers.

The reforms aim to deal with concerns over the way some fares were displayed, in that taxes and additional charges were only added when a purchase was almost complete rather than at the start of the booking process.

\[w.mcclelland\]There have also been worries about the use of pre-ticked boxes, which forced consumers to opt out of taking insurance, for example, and about the advertising of special offers.

Ryanair said it changed its site at the start of April, while easyJet said it would act during summer.