Dr Julian Lewis: Having been born at the mid-point of the 20th century, I think it is appropriate to look at what happened in Anglo-American relations and European-American relations before and after the 1950s. Before the 1950s, we had two opportunities for a world war, and both times a world war took place. From the 1950s onwards, we had one opportunity for another world war, and that world war did not take place.

We can all have theories about why there were world wars between 1914 and 1918 and between 1939 and 1945 and why the cold war did not become world war three. For what it is worth, I will give my theory. In 1914, it was possible for an aggressor to think it could pick off a small state such as Belgium without triggering a conflict from day one with the United States of America. In 1939, it was possible for an aggressor to think it could pick off a small state such as Poland without triggering a world war with the United States from day one. However, from the signing of the NATO treaty in 1949 onwards, it was no longer possible for any aggressor to think it could launch an attack against any European or non-European NATO member state without immediately being at war with the world’s greatest superpower. For me, that is the single most important consideration.​

This debate ought to be about more than the personal qualities of any individual. I would like people to ask themselves this as a matter of conscience: if they knew that it would make a significant difference to bringing on side a new President of the United States of America so that the policies that prevented a conflagration on that scale continue – given he is in some doubt about continuing the alliance that prevented world war three and is our best guarantee of world war three not breaking out in the 21st century – do they really think it is more important to berate him, castigate him and encourage him to retreat into some sort of bunker, rather than to do what the Prime Minister did, perhaps more literally than any of us expected, and take him by the hand to try to lead him down the paths of righteousness? I have no doubt at all about the matter.

What really matters to the future of Europe is that the transatlantic alliance continues and prospers. There is every prospect of that happening provided that we reach out to this inexperienced individual and try to persuade him – there is every chance of persuading him – to continue with the policy pursued by his predecessors.

James Duddridge: I agree entirely with my right hon. Friend. It is right and proper that we are debating the issue, but given his views, why does he support Mr Speaker saying that Trump should not come here? There is a case for that, but it is incongruent with the argument my right hon. Friend is making.

Dr Lewis: I am pleased to say that this is a debate about President Trump and whether he should come here. I believe that it is entirely right that he should come here. Therefore, issues about any extraneous matters are matters for debate perhaps at another time in another place, but not here or now.

Mr Alistair Carmichael: I am grateful to the right hon. Gentleman for giving way, but on what basis does he think giving President Trump a state visit will have the effect he believes? We have already told him he can have one, and just this weekend we hear him again talking about walking away from NATO.

Dr Lewis: I am not at all aware that he has talked about walking away from NATO. On the contrary, he has made two criticisms of NATO. One is that he believes that NATO has adapted insufficiently to meet the threat of international terrorism and is too solely focused on state-versus-state confrontation. The other criticism he has made is – if it is an extreme view, it is one shared by the Defence Select Committee – that countries are not spending enough on defence. He has rightly pointed out, as has his Secretary of Defence, that only five out of 28 NATO countries are paying even the 2% of GDP – which is not a target, but a minimum guideline. The failure of NATO countries to pay to protect themselves has been remarked upon time and again to no effect.

I finish with a point that may be strange to relate, but stranger things have happened in history: it may be that the only way to get NATO countries to pay up what they should in order to get the huge advantage of the American defence contribution – they spend 3.5% of ​their much larger GDP while so many of our NATO fellow member countries do not spend even 2% of their much smaller GDPs – is Donald Trump’s threat. If that is so, Donald Trump, ironically, may end up being the saviour of NATO, not its nemesis.