The ban on flights in English airspace has been extended into Tuesday.
A spokesman for traffic control body Nats said the cloud of volcanic ash is now covering all of the UK.
Planes will remain grounded across England until at least 0100 BST on Tuesday, with further announcements expected later.
The flight ban has left hundreds of thousands of passengers stranded across Europe since the Icelandic volcano erupted on Thursday.
In north-east England, a hastily-chartered North Sea ferry carried 49 stranded passengers from Norway to Tyneside after the local port agreed to arrange the crossing in record time.
The flight ban could also affect two English teams involved in Europa League semi-finals.
Liverpool are due to fly to Spain to play Athletico Madrid and Fulham are scheduled to play in Hamburg on Thursday.
Governing body Uefa says it will make a decision about the matches later in the week.
Cassandra Williams, who had been expecting to start her new job as head teacher in Norfolk on Monday, is among thousands of Britons stranded.
Ms Williams, who is currently in Hong Kong, said: "There are lots of children meant to be taking GCSEs and A levels and they are very worried about when they might be able to fly to get home."
And Karen Abbott, from Southampton, is stuck in Singapore with her husband and daughter, who has diabetes and is insulin-dependent.
She said the family's medication stock is running out.
A statement from Nats said: "Conditions around the movement of the layers of the volcanic ash cloud over the UK remain dynamic.
"Nats is maintaining close dialogue with the Met Office and with the UK's safety regulator, the CAA, in respect of the international civil aviation policy we follow in applying restrictions to use of airspace. We are currently awaiting CAA guidance.
"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."
He added: "We will continue to monitor Met Office information and review our arrangements in line with that. "
Airports across England have been left deserted by the flight ban - but many nearby hotels have seen a boost to business catering for stranded passengers.
Ryanair has grounded most of its planes until 1300 BST on Wednesday.
A Foreign and Commonwealth Office 24-hour consular helpline has been set up on 020 7008 0000 for people stuck abroad.