Simon Calder has been following the dispute and assessing the strike’s likely impact.

Q Just remind me what the dispute is about?

After the bitter cabin crew dispute in 2010, which saw a series of walk-outs, British Airways started recruiting new flying staff on inferior terms. All new recruits at Heathrow are in an operation called Mixed Fleet, which now makes up 28 per cent of the cabin crew. Other Heathrow crew (the “old” lot) are in Eurofleet and Worldwide Fleet.

Mixed Fleet staff are unhappy about what their union, Unite, calls “poverty pay”. Len McCluskey, general secretary of Unite, says: “New entrants to ‘mixed fleet’ are paid a basic of £12,192 per annum” — though British Airways insists it’s checked all the pay slips and the least anyone earned was £21,151.

Unite says that safety is being jeopardised. Over two-thirds of cabin crew surveyed admit to reporting for duty when they were actually unfit to fly because they could not afford to be off sick and lose the allowances involved. And five out of six Mixed Fleet cabin crew reported that their financial circumstances since joining BA have caused “stress and depression”. Some staff have been “sleeping in cars between flights because they could not afford the petrol to get home”.

Q What happened to the last industrial action?

A strike was called for Christmas Day and Boxing Day, then called off a few days before it was due to start when BA made an improved pay offer. But in a ballot conducted just before the New Year, cabin crew rejected that.

Unite says BA refused to extend the option for industrial action for fresh talks to take place; BA says the call from the union came very late in the day.

Q What effect will the strike have?

None on BA services to or from Gatwick, London City or Stansted airports. Mixed Fleet work exclusively at Heathrow.

The way that the airline rosters its staff means that all the crew on a particular flight will be from a single fleet. Furthermore, all flights to each airport are crewed by the same fleet — so the three daily flights to Paris Orly are assigned to Mixed Fleet, while the six trips to Charles de Gaulle are crewed by Eurofleet, who aren’t striking. Key destinations potentially at risk include Helsinki, Lisbon, Moscow, Prague, Vienna and Warsaw, while long-haul Chicago, Las Vegas, Miami, Cape Town, Bangkok, Singapore and Sydney flights are also crewed by mixed fleet. A full list of the routes thought to be affected can be found below.

Q What sort of cancellations are there likely to be?

We won’t know until Friday when British Airways publishes its plans for the two days — it’s possible that disruption could affect Monday and Thursday flights too, to avoid (for example) a situation in which long-haul cabin crew fly out on Monday but stop work on Wednesday. However, BA is likely to protect all its long-haul services: they make the most money, and affect more passengers per flight.

When the last strike was called, BA said it would operate all its services. This time there are more flights to cover, so all it says is that it aims to get everyone where they need to be: “We are looking to ensure that all of our customers, with bookings on those two days, will travel to their destinations.”

Q How will it do that?

There are a range of options, and the plans are likely to include elements from all of them.

The strike is taking place on a Tuesday and a Wednesday, the days when bookings are traditionally lightest. So there will probably be space on rival airlines. In past disputes, BA has chartered in other airlines to operate some flights. Crew might be brought in from Gatwick to cover for Heathrow colleagues. And there are a number of back-office staff who are trained as cabin crew to cover for a variety of causes, and so they could be drafted in.

Q If you have a flight booked and you want certainty, can you change or cancel?

That option isn’t open yet, but it might be by Friday. Before the Christmas strike-that-wasn’t, British Airways said that passengers to potentially affected destinations could switch to flights to nearby airports, or change dates.

Q If your flight is disrupted because of the strike, what your rights?

Passengers whose flights are cancelled are entitled to meals and accommodation until the airline can get them to their destinations; cash compensation is not payable for delays caused by strikes.

Routes believed to be crewed by Mixed Fleet, January 2017

British Airways does not publish lists, and routes shift frequently from one fleet to another — especially at the “seasonal boundaries” between winter and summer timetables. From a range of sources, I have compiled a list that I believe to be correct; please do not rely on it, because I have not had official confirmation of its accuracy.

UK Domestic: Aberdeen, Belfast City, Manchester

Europe: Basel, Bergen, Bologna, Budapest, Dusseldorf, Gibraltar, Gothenburg, Hamburg, Hannover, Helsinki, Kiev, Krakow, Lisbon, Luxembourg, Marseille, Moscow, Oslo, Paris Orly, Pisa, Prague, St Petersburg, Stavanger, Stuttgart, Vienna, Warsaw, Zagreb

US/Canada: Atlanta, Austin, Calgary, Chicago, Houston, Las Vegas, Miami, Philadelphia, San Diego, San Jose, Seattle

Latin America: Santiago

Middle East: Abu Dhabi, Muscat, Tel Aviv

Africa: Abuja, Cairo, Cape Town, Johannesburg, Lagos, Nairobi