Ministers are on red alert that the Icelandic monster could erupt in future creating a doomsday explosion.
Experts say toxic plumes of smoke would quickly fill the skies over the UK and northern Europe, creating climate chaos and killing millions.
The last time it happened, in 1783, crops were wiped out and an estimated 23,000 Brits were killed by breathing air filled with poisonous sulphur dioxide.
The giant ash cloud led to a series of roasting- hot summers and freezing winters.