The UK flights ban has been extended until at least 7am on Monday as the cost to the travel industry of the Icelandic volcanic ash cloud crisis grew.
The further extension to the restriction of flights within controlled UK airspace was announced by air traffic control company Nats.
Nats said: "Conditions around the movement of the layers of the volcanic ash cloud over the UK remain dynamic.
"We are maintaining close dialogue with the Met Office and with the Civil Aviation Authority (CAA) in respect of the international civil aviation policy we follow in applying restrictions to use of airspace. We are currently awaiting CAA guidance."
Nats added: "We are working closely with Government, airports and airlines, and airframe and aero engine manufacturers to get a better understanding of the effects of the ash cloud and to seek solutions.
"We will, of course, continue to make best use of any breaks in the ash cloud to offer opportunities to airlines as they arise."
Nats said it would continue to monitor Met Office information and review its arrangements in line with that.
The further extension of the restrictions means the UK, with the exception of a very few services that have been able to run, has been a "no-fly zone" since around mid-day last Thursday.
Prime Minister Gordon Brown said he wanted airspace to open up as quickly as possible, while Liberal Democrat leader Nick Clegg bemoaned the fact that his children were stuck in central Spain unable to fly home.
As experts put the cost so far to the European travel industry at more than £1 billion, the Foreign Office said it was doing everything possible to help the many thousands of UK travellers unable to get home from abroad.
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