Aer Lingus passengers face a substantial increase in air fares to London after the British Airport Authority (BAA) said it was seeking a 40 per cent rise in landing charges at Heathrow.

The State-owned carrier said it was alarmed at the authority's plans to increase fees, warning that customers would bear the brunt of extra costs.

"We are concerned at this move to increase landing charges as the cost will have to be passed onto to passengers," said a spokeswoman.

The airline's warning came as British Airways said it was prepared to go to court to prevent the authority from raising charges.

BA chief economist Mr Andrew Sentance said it would seek a judicial review if plans were approved for rises over five years in the cost of flying from Heathrow, typically €12 per passenger.

"There is a public interest issue here," he said. "It's a question of whether the public is getting a fair deal."

Mr Sentence was responding to a consultation document from the British Civil Aviation Authority, which said it was considering allowing BAA increase charges at Heathrow, if it kept prices down at Gatwick and Stansted.

Accusing the BAA of engaging in brinkmanship by threatening to cancel work on a €4 billion fifth terminal at Heathrow before it received the extra cash, he said: "Terminal five needs building for the national interest. It is not some thing that should be held to ransom."

Mr Sentance claimed the timing of the authority's assumed fund-raising was flawed, pointing out that the airports operator had already received contributions of £350 million (€546 million) towards the new terminal from airlines. If these factors were taken into account, he insisted that airport charges would fall.

The British Airport Authority has rejected the criticisms.

A spokesman said BAA would have to pay more to raise money than most other companies because its investment programme was particularly big.