Emily Thornberry warned of the danger posed by Russia and Vladimir Putin’s readiness to threaten neighbouring countries.

The shadow Defence Secretary said Putin’s “increasingly strident” approach must be regarded as more than simply “show-boating” at home as she highlighted Russia’s growing military might.

In a sombre speech Thornberry said Putin could now deploy to 150,000 troops within 72 hours and raised the prospect of further attempts to increase his “sphere of influence” following incursions into Crimea and Georgia.

Thornberry’s comments were focussed on the international challenges facing Britain in what will be seen as an attempt to move on from the Labour infighting over Trident.

She drew a stark comparison between Russia’s growing strength and Britain’s cuts to its Armed Forces since 2010.

“Our army is now at its smallest size since the Napoleonic wars. Its size has been cut by a fifth since 2010, and this has been done – as well all know – for purely financial reasons and without proper consideration of the implications…

“Compare the situation today to that of 32 years ago, when Britain sent almost 58,000 troops to take part in a single NATO exercise called Lionheart. Last year, when a major exercise was held in Poland, we managed to send just 800.

“It isn’t just the army that’s still dealing with the cuts announced in the last Parliament. The Royal Navy is relying on a fleet of Destroyers which are liable to break down in the middle of operations because of a sudden power cut. The RAF campaign in Syria and Iraq is dependent on aircraft which are 40 years old – few people’s idea of the best platform in 2016.”

Thornberry , who was speaking at the Royal United Services Institute, largely avoided continuing the debate on Trident but urged people to use “a pragmatic point of view rather than an ideological one”.

Earlier this month Thornberry was savaged by colleagues who complained about her “risible” and “incoherent” speech at a meeting of the Parliamentary Labour Party.

MPs will be voting on whether to renew the UK’s nuclear deterrent later this year.