Irish carrier Aer Lingus has opened a new base at London's Gatwick airport as it seeks to shrug off an increasingly hostile takeover bid from Ryanair and grow its own lost-cost business.

The former state airline said it will operate short-haul services to Ireland and European destinations from Gatwick, its first base outside Ireland, helping to boost its shares more than two per cent to €1.45.

The expansion will cost £100 million in the first year and 120 new jobs will be created. Four Airbus A320 short haul aircraft will initially be based in Gatwick and that is expected to grow to eight within a year.

"The Gatwick operation will complement our existing services out of London Heathrow, and position Aer Lingus for growth as we roll out new routes and bases in future years," chief executive officer Dermot Mannion said in a statement.

Earlier, Ryanair, Europe's biggest budget airline, called on Aer Lingus to clarify its business strategy and prospects, accusing its rival of making "contradictory claims and forecasts".

Ryanair said it was concerned that comments made by Aer Lingus about its trading performance and prospects following the launch of its recent takeover offer were much more upbeat than those made in Aer Lingus's November 11 interim management statement.

"We, as a large shareholder, are concerned about some of these apparently contradictory claims and forecasts, and their impact upon Aer Lingus' forecast post exceptional net profit (loss) after tax for this year and next year," Ryanair said in a shareholder letter to Aer Lingus.

In the letter Ryanair asked Aer Lingus to clarify the impact of increased costs, the loss of revenue arising from the elimination of fuel surcharges and capacity reductions as well as its expected defence fees.

Ryanair officially launched its attempt to take over Aer Lingus last Monday by writing to its smaller rival's shareholders, asking them to accept a €750 million or €1.40-a-share all-cash bid despite the rejection by Aer Lingus's board and management.

Ryanair, which already owns almost 30 per cent of Aer Lingus after a previous takeover attempt, has said other investors should vote in favour of the creation of a united Irish airline by January 5.

Ryanair, whose previous bid in 2006 was blocked by the European Commission on competition grounds, hopes the recent wave of consolidation in the sector will persuade the EU to allow a takeover this time.