The world's busiest international airport told infuriated passengers not to expect full service until Thursday, five days after a five-inch snowstorm turned hundreds of thousands of holiday plans into a nightmare of canceled flights and painful nights on terminal floors.
Travelers' anger boiled over into politics as Britain's prime minister offered to put troops on snow-clearing duty. Europe's top transport official threatened tougher regulation of airports unable to cope with unusually wintry weather.
Prime Minister David Cameron said his government had "offered military assistance" to the company that operates Europe's busiest airport and others in Britain.
But British Transport Secretary Philip Hammond told Sky News that Heathrow operator BAA, owned by Spain's Ferrovial, had turned down the help in clearing snow from runways.
Cameron said that given the exceptional weather, which saw 5 inches of snow fall on Saturday, it was inevitable Heathrow would shut for a time. With a backlog of canceled flights, Heathrow said it would be operating around one third of a normal flight schedule until 6 a.m. on Thursday.
"I am frustrated on behalf of all those affected that it has taken so long for the situation to improve," Cameron said.
Major delays and cancellations persisted at European airports and on the Eurostar train link between the UK and the continent, leaving thousands stranded across Europe as Christmas approached.
European Union transportation commissioner Siim Kallas threatened the possibility of new "minimal service" standards for airports if performance does not improve.
"Better preparedness, in line with what is done in Northern Europe is not an optional extra, it must be planned for and with the necessary investment," he said.
London's Gatwick Airport, which closed overnight due to renewed snowfall, re-opened at 0600 GMT but passengers were told to expect further disruption, delays and cancellations.
Flights to and from Frankfurt airport, continental Europe's biggest, resumed on Tuesday morning after the airport was shut for several hours overnight. "It is our goal to return to normal flight operations as quickly as possible," a spokesman for operator Fraport said.
The picture was slightly brighter for air travelers in Belgium after handling agents at its main airport managed to get hold of de-icing fluid after saying on Monday they might run out, allowing the departure of some planes.
Aviation consultant Chris Yates said that after many years without heavy snowfall, short-term thinking and underinvestment had left Heathrow and dozens of other airports across Britain and Ireland without enough equipment or personnel to cope with big storms.
"They have concluded they don't need snow clearance equipment, so we don't have the capability when bad weather comes in," he said.
He said airport operators in Helsinki, Stockholm and other snowy climes have the equipment and manpower to clear runways within 30 minutes and to remove ice and snow from aircraft stands quickly, while Heathrow lags far behind.
This could be seen in the days after Saturday's snow, when airports in Frankfurt, Prague, Amsterdam and other major cities in mainland Europe bounced back more quickly than Heathrow, where the ice quickly hardened, making removal more difficult.
The terminals at Heathrow were clogged with passengers desperately looking at computer screens to see if they would be able to get to their destinations. So many people were sprawled on the floor that it was difficult to walk.
Some wore Santa hats decorated with vulgar signs making fun of their most un-merry Christmas.
"It's pathetic — you would think this is a third world country," said Janice Phillips, 29, trying to get back to Minneapolis and sitting next to her sleeping boyfriend, head propped up on a backpack with his mouth ajar.
"I've been here for two weeks and all they've been talking about was this snow forecast. You would think the government could do a better job," she added.
Others pointed out that the snow had stopped on Saturday and the airport was still hobbled three days later.
"It's not even snowing!" said Candie Sparks, 19, who was trying to get back to Santa Fe. "It's crazy."
Trains delayedEurostar, which links England to France and Belgium by train, also advised passengers to cancel their trips in the coming days and receive a full refund unless travel was absolutely necessary.
Outside London's Eurostar terminal, the line of travelers waiting for trains snaked several hundred yards from the station, down the street and all the way to the British Library.
Inside, puffy-eyed passengers shuffled across the cold concourse, watching anxiously as the line periodically spurted forward.
One older man played Beethoven's "Ode to Joy" on his harmonica. The crowd livened up when he switched to Europe's "The Final Countdown."
On the rails, Eurostar trains were still operating at reduced speed, with at least one high-speed train crawling along at 12 miles per hour inside the Channel Tunnel.
There were problems in Germany as well. Fresh snowfall forced Frankfurt airport, Germany's biggest, to suspend takeoffs and landings for a few hours early Tuesday — the latest setback to beleaguered pre-Christmas travelers in Europe and beyond.
Frankfurt has seen hundreds of cancellations over recent days — often a result of disruption elsewhere in Europe, including major problems at Heathrow.
In Cologne, two railway workers were killed during the night when they were hit by a train as they tried to de-ice a switch.
Police said the men apparently overheard or heard too late a warning signal from the train driver, the German news agency DAPD reported. No one aboard the train was hurt.
Christmas deliveries at riskThe situation in Brussels eased overnight as a feared shortage of de-icing liquid failed to happen.
More flights than expected were able to take off after the airport managed to secure enough liquid to treat most airplanes departing Tuesday.
The airport had previously warned that it would run out of the liquid — which aircraft may need to land and take off in cold weather — by Monday evening and that it wasn't expecting a new delivery until Wednesday morning.
"Most flights are expected to operate as scheduled, in spite of adverse weather conditions," the airport said on its Twitter feed, although its departure board showed more than half of flights either canceled or delayed.
The icy road conditions in much of Britain also raised doubts about the delivery of Christmas gifts because many side roads were hazardous.
"We are delivering as much as we can, but inevitably some things may not be delivered before Christmas," said Anina Castle, spokeswoman for the Currys chain, which sells computers, iPods, home appliances and many other items.
Currys and many other major businesses have stopped taking online orders for pre-Christmas delivery because of the poor road conditions.