US nuclear deterrent ‘no longer fully credible’, former NATO ambassador warns

At the latest UKTBC Evidence Session on 5 June 2025 defence expert Sir Adam Thomson, who held the role at the North Atlantic Treaty Organisation (NATO) from 2014 to 2016, has today stressed that the “US nuclear deterrent that backs the NATO Article 5 guarantee is no longer fully credible”. 

Speaking at an evidence session of the cross-party UK Trade and Business Commission (UKTBC) of MPs and business leaders, and discussing wider geopolitical tensions, Sir Adam stressed that “the real driver of dramatic change” would be a “US withdrawal from or massive disruption of NATO”.

He suggested that Trump could “perhaps as soon as this month’s summit in the Hague what he wanted to do in 2018 and just pull the United States out of NATO”. 

And Sir Adam stressed: “Even if he doesn’t do that formally he can do it de facto by just refusing… engagement with NATO, exercising, provision of enablers.” 

He warned: “That creates a real crisis, including in the sustained UK and European effort to support Ukraine.”

Recent polling by YouGov for Best for Britain shows that a clear majority (69%) of the public back the UK agreeing to a new defence and security pact with the EU - in order to improve our trading relationship - with just 13% opposed and less than one-in-five (18%) saying ‘don’t know’. 

Sir Adam’s comments come on the same day that NATO defence ministers are meeting in Brussels, with reports UK Prime Minister Sir Keir Starmer will agree to calls to hike UK defence spending to 3.5%, in line with requests from the alliance.  

It also follows the UK’s strategic defence review which was published this Monday.

Naomi Smith, Chief Executive of Best for Britain, commented: 

“This worrying analysis from a former UK ambassador to NATO underlines how crucial the UK’s relationship with Europe is when it comes to keeping the British people safe - and the increasingly unreliability of Trump’s America.

“The government must build on the promise of the UK-EU summit, with a renewed focus on defence. Our polling shows 69% of the UK public support a new defence and security pact with the EU, while access to the EU’s €150 billion defence fund - Security Action for Europe (SAFE) - could boost our homegrown defence industry and support British jobs. Starmer must make this vital agreement a reality.”