Jim Callaghan, Ryanair's director of regulatory affairs, said the offer was designed to keep costs down and improve facilities for its customers.

"We're the largest user of the airport. We're working from the most abject facilities in the airport and we're being charged the same fees as everyone else so that's why we made the request, " he said.

He said a tender process designed to select the most suitable main tenant was never completed, which showed that the DAA was biased against Ryanair throughout the process.

Ryanair will also tell the hearing it believes the DAA is determined to build the most expensive terminal possible to charge airlines higher fees.

"The DAA are pressing ahead with a terminal which is 50% larger than they originally planned and quadruple the cost because this is how they plan to make their money from the current regulatory system, which sets airport fees based on capital expenditure, " said Callaghan.

He said this had increased the overall cost of the project substantially because the DAA will have to spend Euro450m redeveloping the airport's current terminal to reduce the number of passengers it can handle.

Callaghan said this was necessary to meet passenger restrictions imposed Fingal County Council, which stated that no more than 30 million passengers a year could use it.

However, a DAA spokesman said Ryanair had "a semidetached attitude to accuracy and reality" and that Callaghan's comments were inaccurate.

"Our plan from the very start was to build a mixed mode terminal for long-haul and short-haul flights and on the basis that Aer Lingus is our biggest mixed mode customer, they were always going to be the main tenant, " he said.

He said the DAA had employed world-class advisers and detailed traffic projections when building the terminal. "We are building the terminal that Dublin needs to handle up to 35 million passengers by 2018."

He also said the council had placed no passenger restrictions on the airport. "What they said was that when passenger numbers reach 30 million, detailed plans would have to be put in place for a third terminal."