The hon. Lady is right. I am enjoying the consensual nature of this debate—it is the House of Commons at its very best. In 1929, J. F. C. Fuller said that tanks would make infantry redundant. In a sense he was right, but his timeframe was completely wrong, and the infantry was adapted rather than abolished. The imminent end of manned fighters was confidently predicted in a 1957 Government White Paper. The important point, which the hon. Lady was trying to make, is that we cannot base our defence on what we imagine might happen.
The threat of cyber and of unmanned underwater vessels should invigorate our countermeasures and our attempts to detect and potentially disrupt aggressors. Nevertheless, just as the Lightning II joint strike fighter may have only half a life before it is rendered obsolescent, we must be open to the possibility that the Successor submarine may at some point over its long life be made obsolete. However, I do not think that a sufficient argument to deploy against the decision we will make today.
The second proposition that I want to touch on is that of reputation theory. The argument is that unilateralism will in some way raise our standing internationally, but that is hopelessly naive. Try saying that to people in Ukraine; try waving the Budapest memo at them. Many will say that had Ukraine not given up its share of the USSR’s nuclear armamentarium—about a third of it—when it became independent, its territory would now be assured and it would not have been invaded by Russia. I do not want to take that argument too far, because others will make counter arguments about the wisdom of Ukraine having nuclear weapons—personally, I am pleased it does not—but from the perspective of a state that is trying to face down an aggressor, that is a powerful argument.
Some say that if we cut our nuclear arsenal others will follow, but there is no evidence to suggest that that is the case. We have cut our arsenal dramatically in recent years, yet other states have increased theirs.
Finally, in this atmosphere of Brexit, when we are re-forging our links with other international organisations and operating in an outward-facing way that I find refreshing, we must think about our permanent membership of the UN Security Council. That membership is contingent on this country offering something. It may pain some right hon. and hon. Members to ponder this, but in large part our membership of that body is down to our continued possession of this terrible weapon.