British Airways was tonight facing a fresh wave of strikes after a dramatic court victory by the cabin crew union which cleared the way for 15 days of industrial action.
Unite won an appeal against an injunction which blocked a planned five-day walkout this week and later confirmed that strikes will start next Monday.
Cabin crew will take action for five days, followed by further five-day stoppages from May 30-June 3 and from June 5-9, threatening travel chaos for tens of thousands of passengers.
BA said it was "disappointed" with the Court of Appeal's decision, adding that it will implement its contingency plans to keep aircraft flying.
Shares in BA began the day on the front foot but fell sharply after Unite won its appeal and were trading almost 4% lower in a difficult session for the wider market.
The airline is set to unveil a huge £600 million slide into the red for the year to March tomorrow, bringing total losses in the past two years to £1 billion after a £401 million reverse in 2009.
The latest results - the worst since BA was privatised in 1987 - will include an estimated £40 million to £45 million hit from the first round of strikes in March.
The new strikes could cost the firm another £100 million in the current financial year, with Iceland's volcanic ash cloud adding to its woes.
Unite said tonight: "Following today's decision by the Court of Appeal to overturn the injunction restraining strike action at British Airways, Unite the union today confirmed that cabin crew would go on strike for five days from Monday May 24, as previously notified."
Joint general secretaries Derek Simpson and Tony Woodley said: "British Airways management now has a chance over the next three days to address our outstanding concerns and seize the possibility for industrial peace. We hope it has the wisdom to do so."
BA's lawyers said that it would consider the judgment and reserved its position on whether to seek permission to appeal to the Supreme Court.
Two out of three judges in the Court of Appeal in London found in favour of the union, with the Lord Chief Justice, Lord Judge stressing that the court was not making any comment about the merits or otherwise of the industrial action.
"We must all hope for a speedy and fair resolution of this dispute. It must be resolved by negotiation. Legal processes do not constitute mediation. On the contrary they often serve to inflame rather than mollify the feelings of those involved," he said.
Mr Simpson appealed to BA to resume negotiations to try to resolve the bitter row, saying this was not a moment for "triumphalism".
He said there had to be an honourable settlement, stressing that the two outstanding issues of travel concessions and staff suspensions had to be resolved.
"Our reaction is that it is a sensible decision that reflects the minor, almost irrelevant, case that BA tried to bring, and we are grateful that it puts sense into what is an industrial dispute and strikes at the heart of the argument that minor technicalities can set aside ballots like this one which was overwhelmingly in support and democratically conducted by our members."
Mr Simpson said the two sides were "within a slither" of reaching an agreement on the original dispute over jobs, pay and working practices, but the row over travel concessions and suspensions was holding up a deal.
Mr Woodley said: "We are delighted to have won today. Justice has been secured. Had it not been, the right to strike would now be hanging by a thread."
BA said: "We are very disappointed for our customers that Unite's appeal has been upheld and that the union intends to go ahead with its unjustified and pointless strikes.
"We will implement our contingency plan to keep British Airways flying. We are confident that thousands of cabin crew will ignore Unite's strike call and help us fly more than 70% of the customers who were booked to fly with us in the period targeted.
"We will run a full programme at Gatwick and London City. At Heathrow, we will operate more than 60% of our longhaul operation and more than 50% of shorthaul.
"Unite's strikes have failed twice and they will fail again. We have put forward a very fair offer that addresses the concerns Unite has raised over the last 15 months. We believe cabin crew would accept it if it was put to them in a fair and secret ballot."
TUC general secretary Brendan Barber said: "This is an important victory. I hope it marks a halt to the recent run of arbitrary legal judgments where employers have found it all too easy to get courts to find in their favour and prevent employees from exercising their democratic right to take strike action.
Transport Secretary Philip Hammond said: "This decision risks further disruption for passengers. I urge Unite to pause for thought before taking any further action.
"There is still time to resolve this dispute and it is in the interests of the travelling public, British Airways and the cabin crew - whose jobs depend on the future success of the airline - that both sides now urgently get back around the negotiating table."
The conciliation service Acas said: "We have seen the interview with Derek Simpson where he says he hopes that they will be able to enter into talks to resolve this dispute. We also hope that the parties will again enter into talks directly. Acas and its facilities are always available to help if needed."
Corinna Ferguson, legal officer at human rights group Liberty welcomed the "common sense" judgment, adding: "Trade union ballots are there to protect employees, not to allow big business to play technical games in court."