There is, it seems, just one plan in the UK that is equipped to measure the volanic ash in the atmosphere and make judgements on flying safety etc. It's a BAe-146-301 large Atmospheric Research Aircraft belonging to Facility for Atmospheric Measurements.
Where is it? Up in the sky? Nope, it's grounded "with all instruments removed prior to a repaint, and it would take at-least a week to get it airborne and fit for a science flight". What timing!