The Eve of Armageddon — Peter Millar

A British expedition in search of a fabled lost city in the Polar ice cap stumble upon an ancient alien civilization. Transported deep within the earth they discover a race of beings who have been monitoring man's development for millennia. At first the explorers are overawed by the advanced technology and knowledge of the strangers but gradually they find that the aliens are not quite as benevolent as they seemed. What follows is a race against time as the explorers battle to save mankind from being eradicated from the planet.