According to
http://news.bbc.co.uk/2/hi/science/nature/8634276.stm
the new "ash standard" considers 2 mg/m3 as acceptable in place of the unrealistic zero previously. Sound a tad high to me. I would have said a figure like 0.1 mg/m3 might have been OK.
Not sure if I would want to send planes into that soup. OTOH, it appears the ash is "good" ash, with a relatively high melting point. And it would also seem (see the DLR test) that actual concentrations at least around Germany (maybe not the UK) are below 0.1 mg/m3.