An undercover documentary to be broadcast in Britain tonight is set to accuse Ryanair of security lapses, operating dirty aircraft and over-working its staff.
The Channel 4 expose is based on secret videotapes recorded by two reporters who infiltrated the Irish airline for five months posing as cabin crew.
The programme claims passport checks prior to boarding were not carried out properly, new staff were not given the required on-board training and planes were not properly cleaned between flights.
Ryanair is also accused of making cabin crew and pilots work excessive hours, with one pilot saying he feared being sacked if he refused to fly after complaining about being tired.
The Irish airline has rejected most of the claims made in the documentary, saying the relevant aviation authorities have found no evidence to back them up.
It has also promised to investigate what it called "any examples of isolated breaches of Ryanair's own policies and procedures".