Britain must begin preparing for large-scale military mobilisation now, or risk being dangerously unprepared for future conflict, warns a stark new report.
The Royal United Services Institute (Rusi) said the country’s armed forces would need to expand rapidly to meet the growing threat from Russia, cautioning that “the window of orderly action is limited”.
Authors of the report argue that Britain’s land forces may ultimately need to double in size, in what would mark one of the most significant military expansions in decades, GB News reported.
The warning is likely to intensify pressure on ministers, who are already facing criticism over delays in boosting defence spending and long-term planning.
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Paul O’Neill said the UK had missed earlier opportunities to strengthen its mobilisation capability.
“The ideal time to start would have been 10 years ago,” he said. “The next best time is now.”
“Is it going to be too late?” he questioned. “I don’t know.”
“We have a tradition in the UK of doing these things too late.
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.”
He warned that current systems for recruiting, training, and deploying forces are not equipped to handle a rapid scale-up, citing bottlenecks in the existing structure.
“We need to grow the capacity to absorb more reserves, then bring more in,” he said, cautioning that the present model could “choke under pressure” in a crisis.
Britain’s armed forces have shrunk significantly in recent decades. The Army currently has around 73,790 regular soldiers — less than half its size at the end of the Cold War — alongside roughly 31,900 volunteer reservists.
While there are thought to be around 90,000 additional strategic reservists on paper, the report suggests many would be difficult to mobilise in practice due to overlapping roles in civilian sectors.
The think tank also raised the possibility of conscription, though it concluded that a full-scale draft is currently unrealistic given both societal resistance and the military’s limited capacity to train large numbers of recruits.
The report stated: “While meriting consideration, conscription is currently unrealistic, not least because society is not ready for this, and the armed forces could not absorb or adequately train any significant conscript intake or get much military utility from them.
Instead, it suggested that Britain could explore a more limited, selective model, similar to that used in France, as a way of testing mobilisation systems.
The report draws parallels with previous conflicts, noting that the UK has historically been slow to mobilise, often acting only once a crisis is already underway.
Analysts warn that in an era of rising geopolitical tension, such delays could prove far more costly — leaving Britain scrambling to respond at a moment when speed and preparedness are critical.
A Ministry of Defence spokesman said: “We are reversing the four-year decline in Armed Forces recruitment, with more personnel now joining than leaving for the first time since 2020, and female applicants to the Army are at the highest level in five years.
We are taking decisive action on recruitment and retention including giving personnel the largest pay rise in decades, turbocharging improvements to defence housing, scrapping 100 outdated recruitment policies, speeding up the process for those wishing to rejoin the military and appointing the first-ever Armed Forces Commissioner to improve service life.
“The delivery of the first-of-its-kind Strategic Defence Review is backed by the biggest sustained increase in defence spending since the Cold War with £270billion across the Parliament ensuring no return to the hollowed out Armed Forces of the past.”
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