D G Compton & John Gribbin 
Ragnarok [EPUB ebook] 

The day of ice and fire, that brings in its wake devastation to the world. Dr Robert Graham, noted nuclear physicist, has campaigned hard and long for disarmament. Now his patience is at an end. With an ill-assorted handful of desperate, like-minded 'terrorists’, he plans to hold the human race to ransom. His bargaining power is terrifying – nothing short of Ragnarok itself. The world governments must listen – or the countdown to nuclear winter has already begun . . .