Now, instead of a very coarse contour plot, labelled with emotive terms like "low", "medium" and "high", why not produce a fine grained plot with many different numerical values and then allow airlines to generate a safety case relating to the level that they are prepared to accept (if any of this is really necessary vice "see/sense and avoid", in any case)?
Why hasn't this been done? Could it be because the computational power required to generate such a detailed model is not available to the Met Office, or likely anyone else in the meteorological community?
Also, who fancies having a quick sniff of an erupting volcano to have a look at what it's spewing out? Any model is only be as good as the initial conditions, which in this case would require detailed information of what's actually coming out of the volcano (fall rate, particle type/size etc).
Now, is MO'L (or indeed WW in his time at BA) going to cough up the cash to do this? If not, then for now, and no doubt some time to come, we're stuck with the low, medium and high coarse plot, from the existing NAME model the Met Office uses.