That Last Mountain by Terence Strong
Nikolai Shalayez, an eminent Russian mathematician who knows the secrets of the Soviet "Star Wars" defence system, defects to the British whilst on a lecture tour in Sweden. To escape a ruthless Spetsnaz team, with the SAS never far behind, he flees into the icy wilderness. The author has also written "Whisper Who Dares", "The Fifth Hostage", "Conflict of Lions" and "Dragonplague".