Air travellers should not be "too early" for flights from Heathrow over Christmas because they are causing congestion, British Airways has warned.
Passengers will face long waits for check-in if they arrive too early
Passengers should not turn up more than two hours before short-haul flights and three hours before long-hauls, BA said.
The airline warned that there were too many people "milling about" near the concourse before check-in opens.
Busy roads over the festive period and memories of summer delays were causing people to turn up early, BA claimed.
The airport operator BAA is predicting 2.8 million passengers will travel through Heathrow from now until the New Year in the annual Christmas getaway.
A spokesman for BA said people were turning up four or five hours before their flights were scheduled to take off.
He said long queues for security checks owing to a terror alert in August were still in people's minds and were combining with the usual seasonal traffic worries.
"Because it is busy at Christmas, people factor in more time," he said.
"But it doesn't serve them well because they get there so early the self-service kiosks are not open and the check-in is not open for business.
"They are essentially stuck in limbo and are filling up the airport - unable to go through security or go shopping."
Meanwhile, shoppers have been spending on high streets across the country on what is predicted to be one of the busiest trading days of the year.
With recent interest rate rises and the growing popularity of online shopping, there had been fears retailers were facing the toughest Christmas for 25 years.
But the British Retail Consortium said seasonal trade was going "reasonably well".