Strikes by British Airways pilots could disrupt hundreds of thousands of holidaymakers from August after the airline lost a second legal attempt to block industrial action.

The court of appeal on Wednesday upheld last week’s verdict by the high court, which dismissed BA’s claim that the strike ballot was invalid. The pilots’ union, Balpa, can now proceed with planned strikes over pay, as long as it gives two weeks’ notice. The airline carries up to 145,000 passengers a day.

Talks between the union and BA aimed at reaching a compromise restarted on Wednesday afternoon and could continue until Friday.

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“BA’s attempt to defeat the democratic view of their pilots in court, rather than deal with us across the negotiating table, has sadly wasted huge amounts of time and money that could have been put into finding a peaceful resolution,” Balpa’s general secretary, Brian Strutton, said.

“Now the window for negotiation and compromise is closing fast. BA need to wake up to reality. Our ballot returned 93% in favour of strike action. There is a serious issue here and BA has so far refused to help us tackle it.”

A spokesperson for BA said: “We are disappointed that [Balpa] has chosen to threaten the holidays of thousands of our customers this summer with unprecedented strike action. We are very sorry for the disruption Balpa’s strike action will cause our customers.

“While no strike dates have yet been issued by Balpa, and they are required to give us 14 days’ notice of any intention to call strike action, we ask our customers to review their contact details by visiting ba.com, or by contacting their travel agent. We continue to pursue every avenue to find a solution to avoid industrial action and protect our customers’ travel plans.

“Our proposed pay deal of 11.5% over three years is fair and, by contrast to Balpa, has been accepted by the members of the Unite and GMB trade unions, which represent nearly 90% of all British Airways colleagues.”

Ninety-three per cent of BA’s 4,000 pilots voted to take industrial action after rejecting a three-year pay deal. Balpa said it would not announce strike dates until it had held further talks with BA.

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Pilots seek an above-inflation pay settlement that would also include a profit-share scheme, reflecting their argument that they took pay cuts when BA was struggling as a result of the financial crisis and that they should share in the benefit now the business has recovered. BA provided the largest share of its parent company IAG’s €2.9bn (£2.6bn) pre-tax profit in 2018.

BA’s pay offer to pilots of 11.5% over three years has been disputed by Balpa.

Separately, planned strikes by thousands of airport workers could disrupt flights at Heathrow, BA’s main base, with a series of walkouts starting on Friday.