Remarkable – and relatively speaking a blessing – that the wake-up call for Britain to take defence seriously again did not come in the form of a military attack on UK soil, but instead was triggered by the verbal assault of Ukraine’s wartime leader by a sitting US president.

The lack of any physical destruction on British streets, though, should fool no one in government or wider society that the framework of security that has protected the country and its allies since the end of the Second World War is not at best cracked and at worst shattered.

Instead, check out one of the latest posts by Elon Musk, Donald Trump’s “disrupter-in-chief”.

He used his social media site X to say “I agree” with a call for the United States to leave NATO – a transatlantic alliance, and the bedrock of European security, that the new administration had until now continued to back at least in public.

It is yet another example of escalating hostility from the new Trump White House – which has sided with Russia against Ukraine, lashed out at its European partners over their values, and even suggested absorbing Canada as the 51st American state.

The alarming mood-change by a nation that is meant to be a friend surely demands an equally dramatic shift in approach by NATO’s 30 European allies and their Canadian partner.

Rather than stating the obvious – that American support can no longer be taken for granted – they should instead be actively adapting to a world in which it fundamentally no longer exists.

Make no mistake, this would be a daunting and humbling prospect – perhaps too awful even to contemplate, in particular for the UK, which has tied itself militarily so closely to the US for pretty much everything from intelligence sharing and technology to nuclear weapons.

Britain is not alone. All European militaries, as well as Canada, to a greater or lesser extent rely heavily on their more powerful American partners.

Breaking that dependency would require a rapid expansion in military capabilities and capacity across the continent, as well as a huge effort to build up the defence industrial base required to produce weapons at scale and exploit emerging technologies.

Sir Keir Starmer – who is hosting a Ukraine summit of allies on Sunday – has rightly adopted the UK’s natural position of leadership in Europe in the wake of Donald Trump’s extraordinary hostility towards Volodymyr Zelenskyy. He gave the embattled Ukrainian president a warm embrace on Saturday when the two met at Downing Street.

Britain is one of Europe’s two nuclear-armed states, a powerful voice within NATO, and a permanent member of the United Nations Security Council.

But talking tough on defence and the need to support Ukraine as the US steps back is no longer enough in a world where hard power is the only real currency once again.

A pledge by the prime minister to increase defence spending to 2.5% of national income by 2027 and to 3% in the next parliament is of course a step in the right direction.

Yet unless it is accompanied by much greater speed and urgency coupled with a genuinely generational shift in the entire country’s approach to national security then it will go down in history as the headline-grabbing but otherwise empty gesture of a government that has forgotten what it means to be ready to fight wars.

Anneliese Dodds, who quit as international development secretary on Thursday over the prime minister’s plan to fund his increase in defence spending with a raid on the overseas aid budget, summed up the challenge well in her resignation letter.

She wrote that she supported the plan to lift the defence budget but said even 3% “may only be the start, and it will be impossible to raise the substantial resources needed just through tactical cuts to public spending”.

She added: “These are unprecedented times, when strategic decisions for the sake of our country’s security cannot be ducked.”

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Ms Dodds is right.

It is no longer good enough to treat defence, deterrence and wider national resilience as a niche subject that is delivered by an increasingly small, professional military.

Rather, it should once again be at the heart of the thinking of all government departments – from the Treasury and business to health and education – led by the prime minister, his national security adviser and the cabinet secretary.

This is not something new. It was normal during the Cold War years when, after two world wars, the whole country was acutely aware of the need to maintain costly but credible armed forces and a population that was ready to play its part in a crisis.