* Attempts to measure the ash’s density were hampered because the main aircraft used by the Meteorological Office for this purpose had been grounded as it was due to be repainted.
* Computers at the Met Office, which earlier forecast a ‘barbecue summer’ last year and a mild winter for this year, produced a stream of maps predicting the ash would cover a vast area, eventually stretching from Russia to Newfoundland. But across almost all of it, there was virtually no ash at all, and none visible to satellites.
* Though there was some ash over Britain at times during the ban, the maximum density measured by scientists was only about one twentieth of the limit that scientists, the Government, and aircraft and engine manufacturers have now decided is safe.