Vladimir Putin is laying the ground for an assault on NATO territory, which could occur in “as little as six months”, experts have warned. It comes after German Army general Carsten Breuer suggested that Russia could attack land under the Western Alliance’s umbrella in four years. This was mentioned by Andy Marr in the New Statesman's podcast, before the Times' Berlin bureau chief, Oliver Moody, said: "If you believe the Danish intelligence service, it could be as little as six months, according to their latest estimate."

He added: “After the full-scale Russian invasion of Ukraine in February 2022, three days later , the now outgoing German Chancellor, Olaf Scholz, stood up in the Bundestag and announced what he called a Zeitenwende, a turning point in German history, of which the centrepieces were a €100billion rearmament fund, and a commitment to finally meet NATO’s 2% of GDP on defence spending target.”

Mr Moody then said: “And, in fairness to Scholz, he’s done both of those things. The state of equipment and morale in Germany’s armed forces has improved quite significantly. But it is nowhere where it needs to be if it is going to honour its commitments.” Mr Moody then highlighted likely incoming Chancellor Friedrich Merz’s larger €500billion infrastructure spending plan, which includes equipment needed to move tanks and personnel to the Baltic states in a crisis. But divisions remain, including over the prospects of conscription.

The expert went on to say that Russia has a strategy of “industrial-grade sub-military warfare”, whereby “every single non-military tool you can think of has been deployed”.

This includes an “assassination plot” on the Chief Executive of the largest German defence manufacturer, Rheinmetall, and “daily drone incursions” on the country’s military bases.

Moreover, there have been hundreds of cases of sabotage of European railways, a complete bombardment on social media of misinformation and political subversion, including bribery of politicians, Mr Moody said.

The function of this is grounds for debate, as some experts say Putin’s strategy is to make sure Europe remains “unstable” so decision making is more difficult, while others have a “darker” interpretation, suggesting that it “looks like laying the ground for a military invasion”.

NATO General Secretary Mark Rutte told CBS News on Monday that he has urged US and European leaders to increase defence spending and defence industrial production amid concerns of future Russian aggression against Europe.

Mr Rutte also noted that NATO states manufacture four times fewer ammunition rounds than Russia manufactures on its own, despite the fact that its combined economy is 20 times larger.

The Institute for the Study of War (ISW) said last week that it "continues to assess that a strong Ukrainian military backed by Western security guarantees remains the most vital component of a post-war European security architecture, guaranteeing a sustainable peace in Ukraine and deterring future Russian aggression".

Experts added: "Russian demands for Ukraine's 'demilitarisation' such that Ukraine is unable to defend itself against future Russian aggression are counter to US President Donald Trump's efforts to achieve a lasting peace in Ukraine."