There is to be no Christmas truce in the dogfight between Aer Lingus and Ryanair.

In its formal defence against Ryanair's €748m hostile takeover approach, Aer Lingus urged shareholders to ignore what it described as a “rip-off” attempt by the low-cost carrier.

The Aer Lingus rebuff has also been ratcheted up with the announcement that it will restore its Shannon-Heathrow route from next March.

Last week, Aer Lingus also said it would invest £100m in opening a new UK hub at Gatwick Airport, where four aircraft will be located.

Aer Lingus said in Dublin that it expects to move to pre-tax and pre-exceptional profit next year, and possibly for the current year, as cost-cutting measures agreed last month begin to make an impact on its accounts.

It cautioned that 2009 would, however, be a “very tough year” for its short-haul business.

Aer Lingus chairman Colm Barrington and CEO Dermot Mannion reiterated their opposition to the takeover bid, claiming Ryanair is attempting to capitalise on current market fears “to profit from a proven business model”.

Mr Barrington said that Ryanair was “trying to rip off our shareholders” with what he described as a “paltry offer” for the flag carrier.

Ryanair is offering €1.40 per Aer Lingus share, half what it proposed two years ago when it made its first bid. Ryanair owns just under 30% of Aer Lingus, while the Irish government owns slightly over 25%.

Mr Mannion added he had a duty to point out to shareholders that Ryanair's bid faces “a huge competition hurdle”.

But he declined to divulge how much the latest restructuring programme would cost Aer Lingus.

The measures, which will see 200 voluntary redundancies, are expected to generate savings for the group of about €50m.

Ryanair boss Michael O'Leary claimed it was “insulting” to Aer Lingus shareholders to “pretend” the flag carrier is operating at a profit “when it is clearly going to make a substantial net loss this year”.

He added: “Aer Lingus has once again shown it cannot be trusted.

“Aer Lingus claims that it expected to achieve profit overall in 2008 but unfortunately for Aer Lingus shareholders, the reality is that the airline has incurred substantial — as yet undisclosed — exceptional costs.

“Companies have to pay tax, so the result will be another year of substantial net losses.”

Mr O’Leary said he wanted Aer Lingus to answer questions about its net losses in 2008 and 2009.