Just as an aside, I'm not sure why the Met Office is taking flack here. Under ICAO/WMO agreements the MO provide VAAC coverage for northwest Europe. Is that not what they've done? Observe, then forecast, the movement of volcanic ash. Isn't that what's happened?
The information they provide is then used by NATS/CAA etc who then decide whether there can be open airspace or not.
The internationally agreed manufacturers' guidance (before this evening's events) was that there is a zero tolerance for aircraft performance in volcanic ash. Therefore, are aircraft manufacturers not to blame for not knowing what their aircraft limitations are? Where does it end?
Unprecedented is surely the word, and instead of looking to blame people, perhaps learning the lessons and keeping them in mind in the event something like this happens again, is the best way ahead.
If a ban hadn't been put in place, and something had have fallen out of the sky, then the same people claiming over-reaction would be asking why airspace wasn't shut. Lose-Lose.
Edit: Landroger, REAL observations of volcanic ash HAVE been made. By the Finnish Airforce, by KLM (near Eindhoven today), by Lufthansa (just south of Hamburg), by Loganair (this very day, at FL170 above Kirkwall), by parachutists (!!!) at FL030 near Peterborough, by the RAF at Coningsby, by an aircraft approaching Newfoundland......I could go on. There have been plenty, PLENTY of reports of ash in the sky.