Friday is normally the busiest day of the week at Europe’s busiest airport, Heathrow. But a now-cancelled pilots’ strike has led British Airways to cancel hundreds of flights to and from London Heathrow – costing an estimated £20m.

Members of the British Airline Pilots’ Association (Balpa) staged a two-day strike on 9 and 10 September, triggering losses of around £100m. Pilots had also planned to walk out on 27 September, but nine days ago the industrial action was called off.

However, by then BA had cancelled the vast majority of its flights – to give advance warning to passengers, and to avoid paying compensation under European air passengers’ rights rules by providing 14 days’ notice.

After the pilots’ union called off the strike as an olive branch to British Airways, the airline reinstated about half its flights.

But more than 400 services from both Heathrow and Gatwick remain grounded. One reason appears to be the complexities of crewing rosters, and another is the likelihood that many would be half-empty and therefore unprofitable as well as damaging for the environment.

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From Heathrow, the highest number of short-haul cancellations are to Dublin, Edinburgh, Geneva and Nice – with at least 10 BA flights grounded to and from each destination.

On one surviving Edinburgh-London flight today, the lowest fare is £483.

Seven flights to New York from Heathrow, plus another to JFK from Gatwick, will not operate on Friday; the eight inbound arrivals on Saturday are also cancelled.

Other long-haul cancellations include Toronto from both Heathrow and Gatwick, four flights between Heathrow and Mumbai, and links from Heathrow to Dubai, Los Angeles and Washington.

Many flights to destinations served by Thomas Cook until its collapse this week have been grounded, including Corfu, Dalaman and Malaga.

A spokesperson for BA said: “We will operate around half of our flights today, with a schedule of merged services to our daily destinations across our global network.”

On Thursday, the pilots’ union said: “BA pilots believe their management is treating them with contempt and are now asking Balpa to consider more strike dates”.

British Airways pilots strike: Where do we go from here?

On its website, the airline says: “We have not been notified of any further disruption by Balpa pilots.