UK air traffic control company Nats said harmful concentrations of ash were expected to have dispersed overnight.
However, some flights within the UK and a number to Germany will be cancelled.
Germany's Meteorological Service said airspace over the country's northern cities, including Bremen and Hamburg, would close from 0400 BST (0500 local time) because of elevated levels of ash in the atmosphere, prompting cancellations by some airlines in the UK.
They include BA and KLM, which is also cancelling some flights to Norway and Sweden.
Meanwhile, the UK's Met Office said ash might return to affect much of the country on Friday.
Forecasters said that if eruptions from the Grimsvotn volcano continued at "current variables", all areas with the exception of East Anglia and south-west England might be affected by ash, with the potential to disrupt flights.
"On Friday, at between 35,000 and 55,000ft, there could be a risk of a high concentration of ash covering most of the UK," a spokesman said.
The Met Office said the concentration of volcanic ash in the UK's airspace was expected to decrease significantly throughout Wednesday.
On Tuesday, dozens of planes were grounded at UK airports including Glasgow, Edinburgh, Newcastle, Barra, Prestwick, Cumbernauld, Londonderry, Tiree, Carlisle and Durham Tees Valley.
Airports say they are hoping to resume normal services but have warned of possible delays and passengers are advised to check with their airline before travelling.A spokeswoman for Nats said there was no volcanic ash currently predicted for airspace over the UK at a density that would have an impact on flights.
Nats said it would continue to monitor the latest Met Office information and further updates would be provided as and when the situation changed.
The UK's emergency response committee, Cobra, met on Tuesday to discuss the knock-on effects of the ash cloud.
Afterwards Transport Secretary Philip Hammond said that the ash plume had decreased in height and intensity, and south-westerly winds were predicted for the next two days which would move the cloud away from the UK.
The Civil Aviation Authority (CAA) divides the airspace into areas of high-, medium- and low-density ash, and airlines wishing to fly in areas of medium- or high-density ash need to have a safety case accepted by the authority.
It said earlier that, although no airlines had applied to fly in high-density ash, some had been given permission to fly in medium density.
Tuesday's cancellations came just over a year after another volcanic eruption in Iceland caused widespread disruption across Europe, including the closure of UK airspace, amid concerns about the damage volcanic ash could cause to engine aircraft.
The Grimsvotn volcano in Vatnajokull National Park began erupting on Saturday and closed Iceland's airspace for a period.
Experts say the eruption is on a different scale to the one last year and ash particles are larger and, as a result, fall to the ground more quickly.
Icelandic government adviser, Professor Magnus Tumi Gudmundsson said the eruption from the volcano was slowing down "day by day" and he believed the worst was over.
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