Men between certain ages could be called up for conscription amid fresh warnings about the need to prepare Britain for the potential outbreak of World War 3. The Royal United Services Institute (RUSI) has urged the UK Government to scale up recruitment plans as the prospect of war with Russia becomes an increasing possibility. The UK’s leading defence thinktank, founded in 1831, warned that mobilisation will have to go “beyond expanding the volunteer reserves” or recalling Brits who served in the strategic reserve.

In the even of a future conflict, UK conscription would likely follow historical precedents. As World War 2 neared, conscription began for men aged between 20 and 22 in 1939, up to six months before fighting broke out, with the age range widened to any man from 18 to 41-years-old when war was declared. By the end of 1941, men aged up to 51 were being called up for military service, with those aged between 52 and 60 also required to take part in “some form”.

It comes amid repeated calls for military service or conscription to counter concerns over Britain’s ability to defend itself in the event of a third global conflict.

Such calls have been largely driven by fears around the size of the UK’s armed forces compared to Russia, with the latter employing around one million full-time troops, and Britain roughly 140,000.

Several European countries including France and Germany have already moved to bring back forms of military service in response to growing global threats, with many commentators urging Keir Starmer’s government to follow suit.

Paul O’Neill, senior associate fellow at RUSI, told The Sun: “We have a tradition in the UK of doing these things too late.”

He added: “Mobilisation for the First World War and Second World War – typically, it has been late and I can absolutely understand why. Governments do not want to commit to economic costs of mobilisation where they are not confident it is absolutely necessary.

“So I am not trying to be tough on politicians in this regard. But I think we need to start the growth journey now.”

The report recommends that Britain follows in France’s footsteps by initially launching small-scale selective conscription “to see how that works and to flesh out some of the challenges that might be involved” in more widespread implementation.

It also calls for a clear blueprint for wartime mobilisation, including “clearer roles” for veterans and reservists who could rapidly be recalled for service.

The Express has contacted the Ministry of Defence for comment.