I caught a small snippet on the R4 lunchtime news, that Lord Adonis has now admitted the "international" advisors were wrong. He didn't comment the purpose of advisors is to advise, not to compell. The fact does seem to be emerging that the governemnt accepted advice that was wrong, without questioning it, and that it was left to industry (Willie Walsh) to make them face up to their mistake.
Personally, I simply don't have an opinion on whether it is safe to fly aircraft in volcanic ash, it's way beyond my spere of knowledge. But Willie Walsh, for all his faults, does have access to the facts, and he will have experts who understand the safety issues, and concluded it was safe to fly. Assuming he was right, then it's a shame the government didn't have any experts of their own that could have come to the same conclusion sooner.
If Willie Walsh was wrong, and the UK government was right to heed the advisors, then Walsh should of course face life imprisonment for endangering thousands of lives. My personal hunch is that won't be the outcome.