Budget airline Ryanair faced criticism for its internet check-in service after announcing yesterday that its website would be closed for essential maintenance for 10 hours next week.

The Irish no-frills operators last month became the first airline to move to a web-only check-in service which imposes £40 surcharge on any passengers who turn for a flight without having printed off their boarding passes at home.

It asked passengers travelling next Thursday to ensure that they had checked in before 6pm the night before as its website would close between 7pm on Wednesday, June 25 until 5am the following morning.

The Air Transport Users Council, the official watchdog for the aviation industry, said it was "disappointed"

by the move and called on Ryanair to waive the £40 charge for passengers who do not manage to check-in while the website was down.

A spokesman said: "We don't think it is responsible for the airline to switch to a web-only check-in system and then have the website close down for a significant period of time.

"We would certainly want any charges that are incurred as a result of difficulties checking in to be waived.

"We're disappointed that Ryanair has seen necessary to close down its website. Other airlines have not had to close down their websites and we would ask why Ryanair appears to be the only company that requires to close its website to carry out this work."

Ryanair spokesman Stephen McNamara said: "To ensure our website can continue to cater to the enormous demand for our low fares we are undertaking an essential systems upgrade which will temporarily close our site from 19:00hrs Wednesday until 05:00hrs Thursday morning.

"All web check-in passengers who are due to travel this Thursday should check-in and print off their boarding passes before 18:00hrs Wednesday."

Asked whether it would waive charges for passengers who do not check-in online while its website is down, a spokeswoman later added: "Ryanair will review the number of passengers who fail to check-in online and make a decision at that time."