The ban on flights in and out of England's airports, imposed when a cloud of volcanic ash swept across the country, has been overturned.
The Civil Aviation Authority (CAA)confirmed a phased reopening of airports from 2200 BST on Tuesday.
Transport Secretary Lord Adonis said all airports could open again and he expected them to remain so.
The ban has been in place since last Thursday because of fears over the danger posed by the volcanic ash.
The ash cloud was created by a volcanic eruption in Iceland and spread over the UK leading to the closure of airspace across large parts of northern Europe.
A spokesman for BAA, which operates Heathrow Airport, said: "We are ready to open, but until further notice passengers must contact their airline before travelling to the airport.
"Not all flights will operate during the early period of opening, and we will do everything we can to support airlines and get people moving."
Earlier, the air traffic control body Nats had extended the flight ban until 0100 BST on Wednesday.
'Safe to fly'
But Lord Adonis confirmed: "Since the flight restrictions were imposed, the CAA have been working around the clock with the aircraft manufacturing industry, the airlines and the research community to better understand how different concentrations of ash affect aircraft engines.
"As a result, the CAA has now established a wider area in which it is safe to fly, consistent with the framework agreed by the EU transport ministers."
Dame Deirde Hutton, of the CAA, said experts had reassessed the tolerance of aircraft to the ash cloud.
"The major barrier to resuming flight has been understanding tolerance levels of aircraft to ash," the CAA said.
"Manufacturers have now agreed increased tolerance levels in low ash density areas."
The move was welcomed by airlines, which now face the task of getting stranded passengers to their destinations and returning to a normal schedule.
Steve Ridgway, the Chief Executive of Virgin Atlantic, said: "We are working on our contingency plans so that we can resume our scheduled passenger flights and repatriate passengers at the earliest opportunity.
"Whilst the reopening of airspace is good news both for passengers and the industry as a whole it is likely to take several days to get everyone who has been affected to their destinations."
Mr Ridgway's opposite number at British Airways, Willie Walsh, said: "I don't believe it was necessary to impose a blanket ban on all UK airspace last Thursday.
"My personal belief is that we could have safely continued operating for a period of time.
"We are now going to start the difficult task of getting our stranded customers home."
The first BA flight into Heathrow touched down just before 2200 BST from Vancouver.
Both Virgin and BA said they would be working as quickly as possible to "reposition aircraft and crews" and insisted that where flights had been cancelled passengers should not travel to airports.
It has been estimated up to 150,000 Britons have been stranded abroad because of the closure of UK airspace.
A Foreign and Commonwealth Office 24-hour consular helpline has been set up on 020 7008 0000 for people stuck abroad.