The volcano has become more active again in recent weeksParts 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 hit airports in south-east England until Tuesday, it warned.
Transport Secretary Philip Hammond said the situation was "fluid" but that passenger safety was the top priority.
British Airways will discuss the likely impact with air traffic control body, Nats. Airport operator BAA said the situation would be clearer by Sunday.
Ash from the Eyjafjallajokull volcano has caused disruption to thousands of flights since April.
It's good to have information in advance but we are acutely aware that things can change quickly
BAA spokesmanMeanwhile, Italy has fined Irish low-cost airline Ryanair 3m euros (£2.5m) for failing to help some passengers after cancelling their flights during the crisis.
Ministers 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 for Transport said in a statement.
Previous forecasts were only given for the following 18 hours.
Transport Secretary Mr 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.
'No firm details'
A spokesman for BAA, which operates Heathrow, Stansted and Southampton airports in the south of England and Glasgow, Edinburgh and Aberdeen airports in Scotland, welcomed the new five-day forecasts.
Dr Dougal JerramVolcanologist, Durham University
"It's good to have information in advance but we are acutely aware that things can change quickly," he said.
"Over the next 24 hours we'll have a much clearer idea how it will affect southern England," he added.
A British Airways spokesman said: "There is a possibility of some disruption of airspace but we can't give any firm details yet," he said.
"The public will understand if there are some disruptions. It is out of our hands."
BA is facing strike action in the coming days, potentially adding to travel disruption.
Safe-to-fly threshold
Dr Dougal Jerram, a volcanologist from Durham University, warned the last big eruption of Eyjafjallajokull - in the 1820s - went on for around two years, and its current eruption could last "several months".
But he said the continued eruptions would not necessarily cause problems to air travel, as a number of factors - explosive eruptions, a concentrated plume and certain weather patterns - needed to be in place at the same time to create "the perfect storm".
"During the last phase, where it was more explosive, the weather patterns weren't so bad and it wasn't as disruptive as it could be.
"A volcano can be erupting for several years and not cause any problems," he said.
In 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.
But in the past week, several airports in southern Europe have been forced to close and flights have been re-routed.
Italy's civil aviation authority fine on Ryanair comes after it said it knew of 178 cases of passengers who did not receive mandatory assistance, such as food - required under EU regulations - between 17 and 22 April.
Ryanair, which initially insisted it would only refund the cost of passengers' tickets, but later agreed to fully implement European regulations and pay all "reasonable expenses", was not immediately available for comment.
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