Parts of the UK’s airspace are at risk of closure from Sunday because of volcanic activity in Iceland, the Department for Transport has said.
Disruption could affect some of the UK’s busiest airports in south-east England until Tuesday, it warned.
Transport Secretary Philip Hammond said passenger safety was the government’s top priority.
Ash from the Eyjafjallajokull volcano caused disruption to thousands of flights during April.
Airspace across Europe was shut down for five days following concerns that ash could turn to molten glass in high temperatures, crippling plane engines.
Scientists and engineers have since revised the safe to fly threshold, but clouds of volcanic ash have continued to drift over Europe, causing airport closures, flight delays and cancellations.
In the past week, several airports in southern Europe were forced to close and flights were re-routed.
Ministers have agreed on Saturday that five-day ash prediction charts would be made available on the Met Office website.
"Within this timeframe, different parts of UK airspace – including airspace in the South East – are likely to be closed at different times," the Department of Transport said in a statement.
Previous forecasts were only given for the following 18 hours.
Transport Secretary Philip Hammond said the five-day forecasts would ensure "airlines, other transport providers and the public [had] the best possible information".
But he stressed the situation "remained fluid" and the forecasts – based on assumptions about future volcanic activity and prevailing weather conditions – were "always liable to change".
"Nats – the UK’s air traffic services provider – will advise of any airspace closures as and when they become necessary and I urge passengers to check with their airlines before taking any action," he added.
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