Ryanair has once again accused Aer Lingus's board of directors of "illegal and unlawful conduct" in refusing its request for an extraordinary general meeting to consider the closure of the profitable Shannon-Heathrow route.

In a strongly-worded two-page letter to Aer Lingus chairman John Sharman, Ryanair's company secretary, Jim Callaghan, said that the airline's directors were in "continuing breach" of their statutory duties and "remain personally liable" for this.

Mr Callaghan said the claim by Aer Lingus that granting an egm would infringe competition law was "absurd".

"Aer Lingus appears to invoke competition concerns only when it suits your purposes, regardless of how absurd or legally untenable these claims are," he said.

Mr Callaghan added that Ryanair's egm motion would "promote" competition between the two airlines on routes between Shannon and London and removed "any question or possibility of an infringement of competition law".

Mr Callaghan also defended Ryanair's criticisms of Aer Lingus's performance, accusing the directors of presiding over a 20 per cent decline in its share price to €2.40 and a 58 per cent fall in its interim profits to €6 million.

Ryanair said it was still considering legal action against Aer Lingus and its directors for their failure to grant its request for an egm. At Ryanair's annual general meeting last week the airline's chief executive, Michael O'Leary, said the chances of it pursuing legal action against Aer Lingus were about "50-50".

Mr Callaghan was responding to a letter from Mr Sharman on September 17th, which rejected Ryanair's latest attempt to have an egm held to consider the impending closure of the Shannon-Heathrow route. Ryanair is Aer Lingus's biggest shareholder with 29.44 per cent of its shares.

No comment was available from Aer Lingus.