A grim smile crossed my face yesterday morning as Labour’s would-be Foreign Secretary Emily Thornberry struggled on BBC Radio 4’s Today programme to name a single international conflict in which her leader, Jeremy Corbyn, had backed Britain’s armed forces.

Then Thornberry cropped up on ITV’s Good Morning Britain and was asked what Corbyn would do if this country were attacked by an enemy that had unleashed a nuclear warhead. I knew the answer.

Some years ago, Corbyn — a relentless critic of Britain’s Trident nuclear deterrent — was asked if he’d be prepared to ‘press the button’ in retaliation. His answer was no.

The thought of a Labour victory, or a coalition that shunts Mr Corbyn into No 10, fills me with horror. Without a doubt, Britain’s already depleted defence system would be hung out to dry. Over the years, I have watched Corbyn time and again fail to engage with the reality of Britain’s defence needs

That leaves his lieutenants such as the hapless Thornberry in a tricky position.

Yesterday she blithely remarked that she ‘wasn’t prepared to say’ how the Labour leader would respond.

Pressed further by presenter Piers Morgan, she rebuffed him again, insisting that it was ‘best not to say one way or another’ if Labour would ever deploy nuclear weapons.

As a veteran of the Falklands and Iraq wars and a former Chief of the Naval Staff, Ms Thornberry’s unwillingness to engage with the question sent a chill down my spine.

Abject

And as a peer, who has proudly sat on the Labour benches in the Lords since 2007, it left me utterly abject.

Before I was invited to join Gordon Brown’s government, as an expert on counter-terrorism and national security, I had been apolitical, like most members of the Armed Forces.

Thornberry cropped up on ITV’s Good Morning Britain and was asked what Corbyn would do if this country were attacked by an enemy that had unleashed a nuclear warhead. I knew the answer

Indeed, I rarely voted. One of the great strengths of Britain’s military system is that it exists outside the political realm.

Its men and women will obey orders and direction of the elected government of the day — unless they believe these to be illegal — whatever their private views. But the thought of a Labour victory, or a coalition that shunts Mr Corbyn into No 10, fills me with horror.

Without a doubt, Britain’s already depleted defence system would be hung out to dry.

Over the years, I have watched Corbyn time and again fail to engage with the reality of Britain’s defence needs.

He has not merely refused to support the use of our military, whether in peace-keeping missions to Afghanistan and Bosnia or in American-led actions in Iraq and Kuwait (although he did not oppose our 2000 intervention in Sierra Leone), but he has also consistently sided with our enemies, backing those who want to kill our troops.

Corbyn was a cheerleader for the IRA’s campaign of terrorism, crassly inviting convicted Irish Republican volunteers to Westminster three weeks after the Brighton bombing in 1984.

In what could easily be interpreted as an apology for terrorism, he has even described members of the murderous organisations Hamas and Hezbollah as his ‘friends’.

And despite overwhelming evidence that Russian agents were behind the Novichok poison attack in Salisbury last year, which left two people dead and three seriously ill, he notoriously questioned whether the Kremlin was responsible.

Some years ago, Corbyn — a relentless critic of Britain’s Trident nuclear deterrent — was asked if he’d be prepared to ‘press the button’ in retaliation. His answer was no. The nuclear submarine is pictured above

Mr Corbyn, of course, spent most of the Cold War arguing that the Soviet Union had been maligned and he blamed the Russian invasion of Ukraine in 2014 on the West.

In his view, the West is always wrong. He has called for Nato to be disbanded.

Corbyn spent most of the Cold War arguing that the Soviet Union had been maligned. He is pictured visiting a community affected by flooding in Doncaster

It is clear, too, that Corbyn has a deep-seated antipathy to America, rooted in naive anti-imperialism born out of the anti-Vietnam War movement.

That was clear for all to see last year, when, like a petulant child, Corbyn refused to attend a state banquet for the U.S. President when he visited the UK.

After that, how could Corbyn, if he became PM, possibly properly engage in the Anglo-American military briefings that keep our country safe?

It is crucial for a statesman to be able to understand the difference between a man like President Trump and the official role he holds.

Spurning the President would not only spell military disaster, it would also be historically illiterate. Our alliance with the United States has been our strongest and most important international relationship since 1941, and the mutual support of the English-speaking nations has arguably done more for world peace than anything else.

Furthermore, America’s financial support for Nato has been crucial for decades. Europe did not pay for its own defence throughout the Cold War, and does not do so now.

And with the drastic reductions in Britain’s defence budget, these islands are more reliant than ever on America’s protection.

So for Emily Thornberry to be unable to muster any enthusiasm when asked about her leader’s record on defence is understandable.

Radical

To be fair to her, during another radio interview on LBC later that morning, she managed to conjure up one case in which Corbyn backed British military involvement abroad: the low-key intervention by our government as part of a multinational peacemaking taskforce in East Timor, which was seeking independence from Indonesia in 1999.

Conflict in East Timor had been bubbling since the mid-Seventies — and that is significant because it is the decade when Corbyn’s political opinions were set in stone.

It is clear, too, that Corbyn has a deep-seated antipathy to America, rooted in naive anti-imperialism born out of the anti-Vietnam War movement. That was clear for all to see last year, when, like a petulant child, Corbyn refused to attend a state banquet for the U.S. President when he visited the UK

For while much of the world has moved on, he has remained the archetypal student radical whose ideas have never developed or matured; a man-child who has stubbornly refused to change his mind on any point, no matter how overwhelming the evidence.

He is a walking, talking anachronism, capable only of joining marches and protests. Nothing he says or does suggests that he has any understanding of how to lead his party, let alone the country.

He might be able to fire up a rabble with a megaphone at a demonstration or at Glastonbury, but he has been an utter failure at organising an effective Opposition.

And when it comes to this nation’s security — its defence and the intelligence services — you don’t have to be a student of politics to realise that Corbyn’s stance is not just immature but profoundly dangerous to Britain’s safety.

Conflict in East Timor had been bubbling since the mid-Seventies — and that is significant because it is the decade when Corbyn’s political opinions were set in stone. Members of a paramilitary group are pictured above in 1999

Which is why I make no apologies for returning to Corbyn’s continued campaign for scrapping our nuclear deterrent.

What is most bizarre about his position is that, despite publicly supporting the Campaign for Nuclear Disarmament for so many years, he now apparently lacks the courage to voice his own convictions.

Preached

That may be because the trades union movement, on whose patronage Corbyn relies, is opposed to unilateral disarmament — Britain abandoning its nuclear warheads — but in favour of multilateralism (all nations with nuclear fire-power abandoning their missiles).

Since 2017, official Labour policy has been to maintain our Trident nuclear defences. But I don’t believe for a moment that this is Corbyn’s personal opinion.

It flies in the face of everything he has always preached, and he has never been a man to let hard facts alter his views.

Since the collapse of the Soviet Union, Britain’s military planners have had absolute proof of the effectiveness of our nuclear shield.

Declassified plans for a Soviet strike against Western Europe showed the Kremlin was willing to use so-called ‘tactical nuclear bombing’ against Germany, Holland and Belgium.

But the USSR was not prepared to fire nuclear missiles at France or Britain — because we had the power to strike back.

There could be no more vivid illustration of how important it is for the UK to keep Trident.

And there can be no more important reason to keep Jeremy Corbyn out of Downing Street.

Alan West, Baron West of Spithead, has been a Labour peer since June 2007.