Describing the European Commission as "an evil empire", Ryanair's chief executive, Mr Michael O'Leary, denounced yesterday's decision as a bizarre action that sought to overturn 20 years of deregulation and competition in the EU.
"We consider this to be a disaster for consumers. It's a disaster for low-fare travel all over Europe and it's a disaster for state-owned, regional airports," he said.
Addressing a packed press conference a few hundred metres from the Commission headquarters in Brussels, Mr O'Leary dismissed the sum Ryanair might have to repay as "chunk change" but warned that yesterday's decision set a dangerous precedent.
He said that lawyers for airlines such as Air France and Lufthansa were already poring over the Commission's statement in the hope of using it to launch legal action against low-fare airlines.
"They will use this decision as a precedent to prevent competition," he said.
Mr O'Leary rejected the Commission's claim that Ryanair's deal was secret, insisting that, although it was private, its details were leaked to the Belgian press within three months.
"This is the most publicised deal in the history of aviation," he said.
At the heart of his argument - and possibly of Ryanair's legal challenge to the Commission's decision - is Mr O'Leary's claim that the Charleroi deal did not amount to state aid.
He claimed that Charleroi offered similar terms to other airlines and that the airport's move into profitability last year demolishes the Commission's claim that no private investor would have offered such terms.
He said that the deal with Charleroi was similar to a discount arrangement that a supermarket might arrange with its suppliers and that, as such, it was none of the Commission's business.
"There is no requirement of notification. We don't accept that we have received any state aid at Charleroi," Mr O'Leary said.
"All we received was discounts, just like Tesco would receive discounts from its cheese suppliers," he said.
Mr O'Leary said that Ryanair would challenge the Commission's decision at the European Court of Justice, adding that he expected other low-fare carriers and publicly owned regional airports to join the action against the Commission.
He said it was too early to decide about Ryanair's future at Charleroi but that the decision could lead to a reduction in business at the airport.
Mr O'Leary suggested that the longer term impact of the decision could be the acceleration of the privatisation of state-owned airports.
He did not rule out increasing air fares but said the company would do all it could to avoid such a step, perhaps by moving aircraft at Charleroi to privately owned airports elsewhere in Europe.
Rejecting the Commission's claim that it was sympathetic to low-cost carriers, he said that nothing the EU could do would halt the trend towards lower air fares.
"You may not like Ryanair. You may not like our policies or our style but you can't dispute that we've delivered low fares to the consumer," he said.
