Business Opinion: In many ways the most surprising thing about the Dispatches undercover investigation of Ryanair that is due to be screened tonight is that it has taken so long for someone to get around to doing it.

The budget airline has made a virtue out of its meanness and prides itself in an industrial relations culture that is combative to say the least. Add in the fact that some 40 million people fly with the airline every year and it's an obvious target.

And based on the correspondence between itself and the documentary makers, Ryanair was also a juicy target as far as the Dispatches team was concerned.

The initial letter from the programme makers contained a huge number of allegations. (All the correspondence is available on Ryanair.com). They paint a picture of a company so focused on profit that it cuts corners - to a dangerous extent - in areas such as staff training, security and the amount of hours worked by pilots and cabin crew.

Over the next few weeks - the correspondence shows - Ryanair appears to have done a good job of shooting down the allegations.

The extent to which the programme makers accepted Ryanair's answers will become clear when the programme airs tonight on Channel 4.

Many of the allegations are not terribly serious and are little more than confirmation of some of the less attractive aspects of the low cost proposition; grumpy, not terribly helpful staff and dirty planes.

But there are some very serious allegations which relate to security and safety. They include cabin crew not carrying the correct identification and performing tasks for which they were not trained, failing to check passenger's passports etc.

Safety issues include pilots and cabin crew allegedly ignoring fault warnings and most worrying of all, working shift patterns that lead to excessive fatigue.

The undercover reporters claim to have seen cabin crew working 10 hour days for five and six days on the trot. Pilots, the programme makers claimed, complained that "Ryanair's policy is to treat the 100 hours maximum flying time per month for pilots more as a target that a limit".

The problem was compounded by the short haul nature of Ryanair's business and fear on the part of pilots that they will be penalised if they refuse to fly because they are tired, claims the programme.

Ryanair's response was predictably robust with the claims about security passes and passport checks dismissed as "untrue... complete fabrication." and having "no validity".

As regards the issue of cabin crew hours, Ryanair produced the records for the two undercover reporters showing their average working hours were 37 and 30 a week, within the legal limits. Both flew an average of four days a week.

As far as pilots go, Ryanair claims its rostering practice - which has been subject to external vetting - produces "well refreshed and rested pilots".

There were further exchanges of letters from both sides, the upshot of which will become apparent, but based on the correspondence released by Ryanair, it is hard to see the programme doing the airline any lasting damage.

It will, however, highlight the Achilles heel of Ryanair and the other low cots carriers, which is safety.

Along with its peers Ryanair has tested the limits of what passengers will tolerate in the relentless pursuit of lower costs. The results have surprised everybody - even the passengers - who will put up with baggage surcharges, walking in the rain to their planes and the by now mythical pools of vomit if the price is right.

Passengers still assume however that the low cost carriers do not extend their buccaneering ways to safety issues. And there is no reason to believe otherwise given Ryanair's unblemished safety record.

As they point out time and again to Dispatches they comply with - and in many ways exceed - the standards imposed on them by a range of national and international bodies.

But what the Dispatches programme is doing is seriously challenging this assumption that low cost carriers don't compromise on safety issues.

And it is pushing against an open door, with some in the industry arguing that low cost carriers should be subject to different rules which reflect the difference between their business model and those of the more traditional airlines on whose operations the rules are based.

The current regulations - they argue - did not foresee planes turned around in 25 minutes and crews working the sort of shift patterns developed by the low cost carriers.

It is not the sort of thing Ryanair wants to hear. If anything keeps Ryanair chief executive Michael O'Leary awake at night - and one suspects it is a very short list - it is the perception that low cost airlines are some how less safe than traditional carriers gaining any sort of traction in the European public's consciousness.

Not even Ryanair could be sure that seat sales, low prices and O'Leary dressing up in women's clothing could overcome that.