Air space in Scotland and northern England will be opened from 7am tomorrow, NATS, the British air traffic control body, said this afternoon (April 19).
But the authority has kept its ban on flights over much of England until at least 7am tomorrow.
But it said it was hopeful the ban could be fully lifted tomorrow.
NATS said the area of northern England where air space will be open runs north of a line from Teesside in the North East to Blackpool in the North West.
In its latest statement, NATS said the volcanic eruption in Iceland causing the ash cloud had "reduced" and the volcano "is not currently emitting ash to altitudes that will affect the UK".
It added: "Assuming there are no further significant ash emissions we are now looking at a continuously improving situation."
NATS said the weather was "dynamic and changing" and therefore difficult to forecast beyond 7amtomorrow.
But it added: "The latest Met Office advice is that the contaminated area will continue to move south with the possibility that restrictions to airspace above England and Wales, including the London area, may be lifted later tomorrow (Tuesday).
"We will continue to monitor Met Office information and review our arrangements in line with that. We will advise further arrangements at approximately 2100 (local time), today."