The combined official passenger service charge and airport security charge at Cork has increased from 7.85 per passenger in 2002 to 12.60 this year, while at Shannon the charges have increased from 7.85 to 9.50 in the same period.

By contrast, charges at Dublin airport have increased by less during the same period, from 6.55 per passenger in 2002 to 7.70 this year.

These rates are somewhat higher than the average passenger charge figures issued by CAR, which include aircraft parking charges, airbridge rental and runway charges, which are not broken down on a per-passenger basis.

According to CAR, the current average charge at Dublin airport is 6.34; the DAA, while declining to provide detailed current or historical figures, indicated that Cork's average charge is just over 9 while Shannon's is just below 8.

The Commissioner for Aviation Regulation, Cathal Guiomard, admitted that the figures seemed to indicate that he was keeping prices artificially low at Dublin.

"There's no point in having a regulator if prices weren't affected. I have no doubt prices would be higher at Dublin otherwise."

He said setting higher prices at Dublin would ease the pressure on Cork and Shannon airports, which are both struggling financially but "having higher prices everywhere is not preferable".

"Due to the size of the businesses involved, Dublin will always have lower charges because it more passengers to recoup its investments on."

A spokeswoman for the Department of Transport declined to comment on whether the fact that CAR only sets prices at Dublin was starting to distort the Irish aviation market.

"CAR is not responsible for Cork and Shannon because they are not in a dominant position. The issue of an airport setting charges too high is not an issue for them."