A wildcat strike by British Airways service staff has forced the airline to ground all its flights from Heathrow Airport's Terminal One.
BA flights from Terminal One have been cancelled
"Due to unofficial industrial action at London Heathrow by some British Airways staff, all domestic and European flights from Terminal One have been cancelled," a BA spokeswoman said.
About 60 departures and a further 28 inbound services were grounded after BA ticket and baggage handlers staged a walkout at about 1600 BST on Friday, the airline said.
The Transport and General Workers' Union (TGWU) - which represents some BA staff - confirmed that the move had not been put to the vote by its members.
"The strike is unofficial," a TGWU spokeswoman said.
The employees are protesting against a new swipecard entry system, called Automated Time Recording, which allows managers to monitor their working hours.
It is understood staff are worried that the system, due to be introduced on Tuesday, could lead to staff being sent home during quiet periods.
BA denied this, and said swipecards had already been in use in some parts of its Heathrow operations for three years.
The flight cancellations, which came at the start of a weekend during the peak summer holiday season, have caused chaotic scenes at Heathrow, one of the world's busiest airports.
An estimated 10,500 passengers were left stranded, with many complaining that the airline had not done enough to keep them informed.
BBC London News reporter Darshna Soni said Terminal One was "jam-packed."
"There are huge queues alongside each information desk," she said, speaking from the airport.
Tempers frayed as travellers faced the prospect of being forced to spend the night at Heathrow.
"I don't know what the staff's grievance is, but I am very angry at the company for not doing anything for us," said passenger Alec McIntyre, who had been booked on a flight to Aberdeen.
Flights from Terminal One serve destinations in the UK and mainland Europe.
BA flights from Terminal Four, which fly to long-haul destinations, are unaffected, the airline said.
BA has issued an apology to passengers, and has advised anyone planning to fly from Terminal One on Friday evening not to come to Heathrow.
It is urging passengers to call 0800 727 800 for further information instead.