Putin’s brutal invasion of Ukraine has now entered its third month and a new phase. He underestimated the Ukrainian resolve to fight and has been forced back to focus on the east of the country. For now.

Whatever Putin gains in the short term, we must ensure he fails in the long run. This means recognising Ukraine is only part of a broader strategy for Putin’s Russia, as he seeks to re-establish a sphere of control between Russia and the West. The annexation of Crimea and support for proxies in the Donbas in 2014 were staging posts for this year’s full-scale attack. Not once during Putin’s time in office has “temporarily occupied” territory been relinquished.

We need to shift now from crisis management in response to the current conflict in Donbas to delivering the medium-term military support Ukraine will need for Putin’s next offensive on Odesa or Kyiv, and thinking longer term about how the strategy for European security must change.

Ukraine reminds us that the greatest threat to UK security lies in Europe, the North Atlantic and the Arctic. It reinforces Nato as our primary UK security obligation. When Boris Johnson trumpeted his Integrated Review last year as having an “Indo-Pacific tilt”, there was no section on Europe and no mention of a Taliban takeover in Afghanistan or invasion of Ukraine. “Global Britain” was in fact a plan for “Go It Alone” Britain.

Yet almost no nation can do anything alone, and Britain is a bigger force for good in the world when we act with allies. The response to Putin’s invasion of Ukraine has been effective due to the strength of Western unity to co-ordinate military assistance, introduce sanctions and bolster the borders of Nato allies.

Nato has proved such a powerful security alliance because it pools military capacity, capability and cash, with an annual budget of more than $1 trillion to protect one billion people. Faced with fresh Russian aggression, that’s why Finland and Sweden are set to join.

Labour is the party of Nato. All wings of our party supported its formation more than 70 years ago, and I am proud of the leading role Attlee’s government played in forging this successful post-war pact. Labour values are embedded at the heart of the alliance, with its founding treaty enshrining democracy, freedom, peace and the rule of law, as well as collective security. It embodies British and Labour internationalism at its best.

In an age of growing autocracy, we must also remember that it is this group of democracies that guarantees our security and Article 5 is the cornerstone of our defence.

Since the start, the UK has long been the leading European Nato nation, and Nato’s Allied Maritime Command in Northwood is an important part of this. When I visit the base today, I will thank the British personnel stationed there and underline Labour’s unshakeable commitment to the alliance.

I will also stress the need for stronger UK leadership to anticipate the likely next areas of Russian aggression, including the Baltic and the High North. As a North Atlantic nation with a world-class maritime military, the UK should lead Nato’s strategic response as the Arctic opens up and China and Russia expand their influence. The current Nato Strategic Concept set in 2010 does not mention the Arctic once, and UK ministers should press for Nato’s new strategic plan, due in June, to incorporate these threats.

However, our leadership in Nato could be at risk as Britain falls behind allies in responding to the Ukraine invasion. More than a dozen European countries are now rebooting security plans, but the UK government has refused to revisit flaws in the Integrated Review. Labour has argued for a new security white paper by the end of June to revise our defence plans to deal with the new threats to UK and European security.

As Nato’s posture develops to give greater focus to defence, alongside deterrence and diplomacy, the UK should be driving these debates. Now is the time to demonstrate Britain really is Nato’s leading European nation, as we will be dealing with the consequences of Putin’s war for many years to come.

John Healey is shadow secretary of state for defence of the United Kingdom