Christmas travellers have been facing up to spending the festive holiday away from their families after forecasters said there is no thaw in sight before Boxing Day.
Heathrow was operating no more than a third of scheduled flights with just one runway open, while at Gatwick planes were grounded until 6am.
Both airports were warning of delays and cancellations as the big freeze maintained its grip.
There were also more long queues for Eurostar passengers at St Pancras station in London, after thousands were forced to wait for up to eight hours on Monday in bitterly cold weather.
Eurostar said speed restrictions were in place on its high speed lines, adding up to two hours to journey times.
Meanwhile, East Coast trains to and from London King's Cross were suspended, severing one of the UK's main rail arteries.
BAA chief executive Colin Matthews defended Heathrow's response to the crisis and said the airport got off to a "good start" on Tuesday morning.
"We have got as many contractors as we can use, in addition to our own staff, clearing the snow," he told BBC Breakfast.
Passengers were urged to check the airport website to see if their flight was listed for departure.