BBC News with Fiona McDonald

The disruption of air travel caused by the spread of volcanic ash from Iceland has worsened with no flights leaving or landing at airports in northern and central Europe. At least 23 countries closed their airspace in whole or in part on Saturday. Three quarters of transatlantic flights were cancelled as the clouds of ash and dust move further across the continent. With the weather and the wind direction unlikely to change, little improvement is predicted for the next 24 hours. Doctor Matthew Roberts from the Icelandic Meteorological Office explains.

"There still is a tremendous quantity of ice for melting via the erupting volcano. And the reason why the glacial ice is so important is that the glacial ice is responsible for quenching the lava that's appearing at the eruption site. As it quenches, it cools, fragments into tiny but abrasive shard and this material has been lofted high into the atmosphere and is traveling towards Europe."

A test flight is being carried out in Dutch airspace to assess the impact of the volcanic ash on aircraft parts. Officials said the aircraft belonging to the Dutch carrier KLM would fly at lowerer altitude than usual to try to avoid flying through the massive ash cloud.

Tens of thousands of people have attended an open-air memorial service in the Polish capital Warsaw for President Lech Kaczynski and 95 others who died in a plane clash in Russia. Duncan Kennedy sent this report.