All commercial flights were scrapped yesterday after the Eyjafjallajokull volcano, situated under a glacier, sent a noxious dust-cloud drifting South across Europe.
Flight delays are now expected to last for several days as all of the major carriers deal with the backlog.
A spokeswoman for air traffic control body, Nats, called the freak occurrence “the most significant incident in the history of flight disruption in the UK.”
She said: “It is unprecedented in living memory for a volcanic eruption to cause this scale of disruption. It is a unique incident.”
Nats decided to lock-down UK airspace amid fears the dust could destroy the engines of planes flying through it.
Commercial flights were still grounded at 7am this morning, when regulators will rule on whether it is safe for them to commence.
Even following the 11 September attacks, a limited number of flights were allowed to continue to their destinations.
British Airways estimated at least 600 flights out of the UK were cancelled yesterday. The lost flying day follows a week of strike action at the company last month.
However, analysts told City A.M. the eruption is unlikely to have a long-lasting affect on the airline.
Derek Mitchell of Royal London Asset Management said: “The public will be forgiving over this. It is certainly less damaging than the strike action. It is likely this type of event will be covered on its insurance.”
Air traffic was also shut down in Belgium, Holland, Denmark, Norway and northern parts of Finland and Russia.
It is the second time in a month the Icelandic volcano has erupted.