Nigel
My machines did continue to work and no, there were no engine problems.
The point was that Class A air space closed on the basis of a mathematical model of location / density of ash. The actual location / density of ash did not match the model and hence no problems for those that did fly in the S. of England outside of actual ash contamination.
I have no idea whether anyone did fly a turbine helicopter through ash, but I don't fancy that one myself. abrasion of rotors would be significant, windscreen abrasion and all of the engine problems / risks (in a single)?