Plans for a fresh ballot of British Airways cabin crew are at an "advanced stage", it was revealed today as staff took part in the final phase of the current wave of industrial action.

Members of Unite walked out for the 22nd day today in the long-running dispute which has cost the carrier more than £150 million, with further action threatened for the summer unless the deadlock is broken.

Assistant general secretary Len McCluskey told a noisy rally of strikers near Heathrow airport that the "fight for justice" would continue, adding that preparations for a fresh ballot were at an advanced stage.

He said the blame for the continuing instability at the airline must be placed "firmly" at the door of BA management's "tough guy" stance.

Mr McCluskey said: "Comments about holding out for as long as it takes against the workforce should cause despair among BA board and shareholders.

"While Unite views this as a process where both parties must compromise, BA's chief executive prefers to see this as a siege against his own workforce.

"This bunker mentality suggests that the true objective is not cutting costs, but crushing the workforce. Talking tough will not help find peace."

Mr McCluskey said the City should scrutinise the airline's claims about its strike-breaking operation more carefully, adding: "The question shareholders and the City must ask themselves is, not how many planes took off, but how many passengers actually flew on BA flights?

"Planes were empty because passengers were enjoying the hospitality of competitors, and BA paid them for the privilege. The jewel in BA's crown, Terminal 5, has taken a heavy hit as there are no passengers to enjoy the shop, and forward bookings are taking a huge hit as passengers reject Willie Walsh's vision for BA.

"This is not successful contingency planning, this is ruination. If BA had nothing to hide, then they should throw open their books and show exactly what this cost. The City must wise up to the BA con trick."

Mr McCluskey praised the cabin crew who took strike action, saying they had faced "unprecedented" intimidation, continuing: "It is been like you've done 15 rounds with Mike Tyson - and you're still standing. Not only are you still standing, but unless BA resolves this dispute, you're up for a rematch.

"The intimidation crew have faced has been unprecedented, yet over 22 days they have stood tall and remained dignified. They can go back to work with their heads held high. They may be bullied but they will never be bowed by BA."

Labour MP John McDonnell, who pulled out of the party's leadership contest earlier today, told the rally: "My message to you is a simple one - thank you. You have shown that people will get off their knees and stand up for what is right. You have won the admiration of the whole community."

The two sides continued to clash over the impact of the strikes, with BA insisting it was running 80% of long-haul flights from Heathrow despite the industrial action, while Unite claimed that BA failed to operate 43% of its reduced schedule yesterday.

BA maintained it ran more services during the current five-day walkout, saying more crew had turned up for work.

A number of striking cabin crew told MPs yesterday there was a "climate of fear" at the airline, as they explained their side of the row.

Unite said about 60 crew members had now been suspended and eight sacked in recent weeks, mainly for "trivial reasons", and has accused the airline of a "crackdown" on union members.

BA has strongly denied the charge, maintaining it was duty-bound to follow its disciplinary code.

BA has been aiming to operate around 80% of long-haul flights from Heathrow despite the strikes, up from 70% and 60% in the past two strike periods, and 60% of short-haul flights, up from 55% and 50%.

BA said it was slashing Club World business-class fares by up to £900 and selected first-class fares by more than £1,500 in its premium leisure sale starting tomorrow.

Chief executive Willie Walsh said: "Customers can take advantage of these great discounts with confidence. We recognise that some may be concerned about the possibility of future disruption but it is our intention to keep flying 100% of our long-haul operation throughout the coming months. We will keep the flag flying."

The conciliation service Acas has said it expects a date to be set shortly for peace talks to resume.