It is a stupid lawyer-ish over-reaction. I am sure there is zero risk to any aviation anywhere in Europe - so long as the plume coming out of the volcano is avoided (which is easy; everybody knows where that is).
The amazing thing is that the airspace owners have been able to shut everything down without having evidence of the risk to aircraft and without even making an apparent effort to find out. I reckon they are going to get sued big-time by the airlines. I hope they do get sued.