The British Airways cabin crew strike entered its third day today amid speculation the airline is preparing another court bid to halt the latest wave of walkouts.

BA has written to union Unite warning its legal battle against the stoppages will “come to a full court case in due course”, and for its officials to keep all relevant paperwork ahead of “pending court cases”.

The union successfully overturned an injunction blocking the strike last week, ushering in the first of a series of five day strikes on Monday which have disrupted travel plans for thousands of passengers.

A spokesman for BA said: “We are not appealing the court’s decision. The union would have been fully aware that the point of law over the communication of the strike ballot result would come to a full court case in due course.

“We have written to Unite to remind them to retain relevant paperwork. This is standard legal procedure for all pending court cases.”

Unite joint leader Derek Simpson posted a message on website Twitter yesterday, saying: “BA to pursue it’s trivial legal point further .. Obviously Willy (Walsh, chief executive of BA) doesn’t like to be bested but somebody at BA needs to get a grip of him.”

Yesterday the union’s leaders issued a fresh plea to resolve the bitter dispute after claiming that the series of strikes had now cost the airline £63 million.

Tony Woodley, joint leader, also warned that BA would lose business when passengers “look elsewhere” for flights during the peak summer period.

Union members said the walkout was being strongly supported, with short-haul and long-haul flights being grounded.

But BA countered that it had more crew than it needed to operate its contingency schedule and as a result was adding flights.

“The numbers of cabin crew reporting at Heathrow are still at the levels we need to operate our published schedule and Gatwick cabin crew continue to report as normal.

“We are carrying more than 60,000 customers a day throughout the industrial action and we are keeping the flag flying.

“We continue to fly a full normal schedule at Gatwick and London City Airports. At Heathrow we continue to fly more than 60% of our long-haul flights and more than 50% of our short-haul flights,” the airline said.

The two sides remain in dispute over travel concessions taken away from staff who went on strike in March, and over disciplinary action taken against dozens of union members.

Unite is planning two further five-day strikes unless the deadlock is broken.