Was Flight Ban Over Ash an Overreaction?

HaymarketRiot writes "Richard Branson has claimed that the flight ban, due to the eruption of the volcano Eyjafjallajokull, was an overreaction on the part of the authorities. Britain's government has even called for the airlines to be compensated. This does look like a perfect excuse for already greedy airlines to try and get more money ... any experts care to comment on the effect of volcanic ash on planes?"