The DAA has refused to confirm the figure, which equates to over 9% of total group expenditure and was described as staggering by one of the leading opponents of the Terminal 2 project, Ryanair.

The revelation comes as it emerged the DAA has sought talks with unions at its airports over its Christmas bonus scheme, which was worth on average around 1,500 per employee last year. Union sources believe the company will seek a reduction in the scheme, which costs it around 4m a year.

A DAA spokesman refused to comment on the company's plans to change the bonus scheme and said the DAA did not comment on the fees it paid its consultants. However, he said that a significant portion of the consultancy fees were incurred last year"due to the specific planning, design and architecture requirements involved".

He confirmed that the company was employing 60 full-time consultants for the next three years on its Terminal 2 project. He added that the DAA put its contracts to open, competitive tender processes "that ensure the company obtains the most appropriate balance of expertise and value in each case".

However, Ryanair's head of regulatory affairs, Jim Callaghan, said the DAA was wasting money and that Ryanair had spent less than 1m on consultants for its alternative proposal for a low-cost Terminal 2.

"These guys are wasting as much money as they can because, under the regulatory regime, they get a return on what they spend, " he said. "We were still arguing [with the DAA] over the cost of the terminal and now there's another 47m we weren't aware of, which makes the cost close to 900m."