My hon. Friend is right. We have made that point clear. It is now agreed between both sides—which is important to my argument — that both the Soviet Union and the United States of America have been indulging in that form of research. They have not even contended that they are not doing so. It is not a peripheral matter—it is a key component of what the Soviet Union is doing.

The explanation for that is, I believe, self-evident. The Soviet Union wishes to explore the scope that new technologies might offer for an effective, active defence of the Soviet homeland against nuclear attack—defence against ballistic missiles which would complement the substantial effort which, unlike the West, the Soviet Union has already been putting into civil defence and defence against aircraft.

Let me emphasise that I am not arguing that the Soviet Union is about to deploy such a defence or that there is an intention at this time to do so in the future. It is, perhaps, simply a question of it keeping its options open. What is incontrovertible is that the Soviet Union has not accepted for all time the existing relationship between offensive and defensive forces at the nuclear level.