The strike, by 2,900 members of the Unite trade union, is in pursuit of higher pay for members of the so-called "mixed fleet".

Those are staff who have been recruited by BA since 2011, and who are paid what the union calls "poverty wages".

BA says most flights from Heathrow will not be affected, nor will any flights from Gatwick and London City airports.

A spokesman for Unite, Oliver Richardson, said: "The 'mixed fleet' cabin crew are at breaking point over pay levels which are forcing many of them to take a second job or turn up to work unfit to fly.

"With the parent company of British Airways forecasting annual profits in the region of £2.3bn, it's clear that the UK's national carrier can pay the people who keep us safe while we fly a decent wage," he added.
Stance

Behind the scenes there has been further contact between the airline and Unite, but nothing strong enough to defuse the dispute.

If the two-day strikes see no change in the airline's stance the union will take stock and it could, in line with its ballot, call further strikes or other forms of industrial action.

BA has downplayed the likely impact of the strike, saying only that a few of its Heathrow flights will be combined, so some passengers will have to fly out slightly earlier or later than planned.

But the company has refused to increase its pay offer further in the face of the impending union action.

A pay rise of 2% in the first year, and 2.5% in years two and three, was rejected by a vote of 7-1 among Unite members, after it was tabled shortly before Christmas.

The union said that that increase would have left staff only £20 a month better off after tax.
Dispute

BA created the mixed fleet of cabin staff in the wake of a bitter and long-running dispute over pay and conditions for all cabin staff that ran from 2009 to 2011.

The mixed fleet staff employed since then, currently about 4,500-strong, are on inferior pay and conditions to those cabin staff who were recruited in previous years.

They fly only out of Heathrow, and on both short-haul and long-haul routes, but not in the same planes as colleagues on the legacy conditions of employment.

Unite complains that despite the airline advertising that the mixed fleet staff are paid between £21,000 and £25,000 per year, in reality their earnings are far lower, typically starting at just over £12,000 - plus £3 an hour flying pay to cover expenses such as paying for food.

BA disputes these figures, and insists that full-time mixed fleet cabin crew do, in reality, earn above £21,000.

Striking staff are expected to gather at Unite's office at Heathrow and then picket at certain points around the huge airport complex.