Britain’s ageing population is not a distant concern, it is our demographic reality. It reshapes the economy, the tax base, the workforce, and the expectations placed on public services. It also reshapes defence: who can serve, who needs protecting, and how we prepare for future crises.

Now though, the move to increase military spending and expand the armed forces begs questions of where all this sits within the context of an ageing society.

A new fiscal battlefield

An ageing population isn’t just a social issue, it’s a fiscal one. According to the ILC’s Route Map for Long Lives, the proportion of UK adults aged 65 and over is rising steadily and is projected to reach nearly a third of the population by 2040. This shift will have a substantial impact on pensions, long-term care, the NHS, and the broader economy. Longer lives bring a number of opportunities: the retention of skills in the workforce and the strengthening of communities, for example. Adapting to this change requires investment now, with long-term consequences if we don’t focus more on prevention and healthy ageing. This includes funding for housing, training and local services that underpin resilience at home.

At the same time, we have committed to increasing defence spending to 2.5% of GDP by 2027. The consequences of this are already apparent. Increases in defence budgets have come alongside reductions in overseas aid and welfare spending, including disability benefits. Every pound spent on tanks, drones, or aircraft is a pound not spent on social care, district nurses, or community rehabilitation. When public funds are limited, there is no escaping such trade-offs – they are uncomfortable, but they are real.

This isn’t a false binary: defence and welfare are both essential. But it does demand honesty. If we want to prepare for tomorrow’s wars, we must also prepare for tomorrow’s (ageing) society. We need defence policies that are realistic of the fact that more people are older, and longevity strategies must consider how security risks might affect people of all ages.

Recruitment and retention

If funding is one challenge, manpower is another. Britain’s armed forces already face recruitment and retention issues. The British Army has missed its recruitment targets for several years in a row, with intake 25% below target in 2022–23; RAF aircraft numbers dropped by 22% in the seven years up to 2023; and the navy was so short on recruits that some vessels have been removed from service.

The total number of full-time active personnel has declined from over 200,000 in 2000 to just over 148,230 as of April 2024. The average age across the UK’s armed forces has remained relatively constant over the last 10 or 20 years but has increased slightly – the average age of those serving in the Army in 2024 was 31 years compared to 30 in 2015. However, a brief look at the proportion of personnel by age group rather than overall mean figures suggests that there are issues around retention as much as recruitment and in 2024, 1,980 people more personnel left the services than joined it – a net decrease of 15%.

There are numerous elements to the overall attractiveness of military service, such as salary, benefits, issues with accommodation, as well as perceived and actual risks, all contributing to this drop-off. Nonetheless, demography is not on the side of traditional recruitment practices. Falling birth rates mean fewer young people overall, while rising obesity, mental health issues, and chronic conditions among under-25s mean that even within that group, fewer meet military fitness standards.

The European Defence Agency has also highlighted this issue across Europe: a shrinking pool of eligible recruits, not just due to numbers, but due to medical and psychological ineligibility. This trend is forcing a rethink. Should we relax age or medical criteria? Open up new support and cyber roles? Reconsider what “fitness” should look like in a 21st-century force?

The alternative is a recruitment crisis, not just in combat arms, but across logistics, intelligence, engineering, and command structures. Without reform, shortages are inevitable.

The “Old Man’s War” – a strategic trade-off

In Ukraine, the demographic dilemma is being played out in real time, but not in the way many might assume. Despite the brutal toll of war, the Ukrainian government has been reluctant to undertake mass conscription of younger citizens. The calculation being that recruiting en masse from the under-25s would have profound economic and social consequences, disrupting education, hollowing out key sectors, and potentially eroding public support.

Instead, the conscription net has been cast wider among older men. Those in their 30s, 40s or older – some trained decades ago, others with no prior military experience – have been called up. This is the product of a painful balancing act: preserving the long-term social and economic fabric of the country while meeting the immediate demands of the battlefield.

There are clear risks. Older recruits often face greater physical challenges, and the demand for replacements on the frontline means that Ukrainian forces never quite have enough people when they need them; even so, while mobilisation is never as extensive as might be needed, it has still outpaced the supply of adequate centralised training.

Yet necessity has also driven innovation. Interestingly, certain Ukrainian units have begun recruiting directly, drawing on the knowledge and experience of veterans to offer better training and provide new recruits with more choice in role assignment. While these practices vary by unit, they reflect a level of innovation in recruitment that could offer valuable lessons for the UK. If managed carefully, older age cohorts could be part of a broader strategy to sustain operational capacity, without undermining societal resilience.

Redefining who is fit to serve

While Ukraine adapts, the UK still relies on rigid medical exclusion policies. Take Huntington’s disease, for example. At present, individuals who test positive for the gene, regardless of symptoms, are barred from serving. The Huntington’s Disease Association argues this is overly restrictive, given that many such individuals are healthy and capable of service for years, or even decades before symptoms become apparent.

This is about more than one condition. It’s about whether the military can afford to keep excluding willing, capable people based on a blanket approach to risk. As recruitment pressures mount, a more personalised, evidence-based policy could help.

The Ministry of Defence, however, confirmed in May 2023 that there are no current plans to amend the policy. Yet that was two years and a General Election ago when the world looked very different, and across many sectors – from policing to aviation to emergency response – we already see roles being adapted to individual medical needs. Defence should be no exception.

When civilians become the front line

It should also be noted that warfare inherently blurs the line between front and rear. Civilians, particularly older ones, often face the harshest realities. In Ukraine, thousands of older people have been unable or unwilling to evacuate war zones due to frailty, lack of support, or deep emotional attachments to their homes. Some have died in their homes, others cut off from medical care or basic supplies.

In emergencies, older people often struggle to access basic necessities. An assessment by HelpAge found that:

• 64% did not have enough to eat
• 77% had no income
• 20% lacked shelter
• 25% had no access to safe drinking water
• 62% lacked bathing facilities

The UK must take this seriously. In any future crisis, be it military, environmental, or cyber-related, older people will be among the most at-risk. Civil resilience planning must factor in age: from accessible emergency shelters to evacuation procedures and health system continuity. Older populations are not passive recipients of care; they are citizens with rights, needs, and, often, deep social and community roles.

A defence policy that ages gracefully?

A forward-looking strategy must do several things. It must rebalance military investment with that in health, care, housing and skills. It must rethink who is eligible to serve, based on ability rather than assumption, and how recruitment is approached. It must design civil defence systems that include the old, not just the fit and mobile. And it must draw lessons from Ukraine, not just on firepower, but on flexibility.

Health, housing, social care and security do not sit in isolation. If we want to defend Britain in the decades to come, we must learn to defend an ageing society.

References

1. One hundred not out: A route map for long lives, ILC December 2023
2. IFS, The Size and Shape of the UK State, 2023.
3. Ministry of Defence, Integrated Review Refresh, 2023.
4. UK Defence Journal, RAF aircraft numbers drop by 22% in seven years, 2024
5. Navy Outlook, Is the Royal Navy in a terminal or temporary decline, 2024
6. UK Parliament Defence Committee, Recruitment and Retention in the Armed Forces, 2023.
7. Average age of personnel in the armed forces of the United Kingdom in 2024, by military branch and rank, Statista, 2024
8. House of Commons Library Research briefing UK defence personnel statistics. Published Tuesday, 13 August 2024
9. MOD Quarterly service personnel statistics: 1 January 2025 – published 20 February 2025
10. European Defence Agency (EDA), Defence Data 2022.
11. The Guardian, Ukraine’s Old Man’s War, 2023.
12. The Kyiv Independent, As US pushes Ukraine to lower conscription age, why won’t Kyiv draft younger men? December 2024
13. The Kyiv Independent, Ukraine reforming recruitment system to attract 18-25-year-olds, January 2025
14. Forbes, Ukraine’s Newest Leopard 2 Brigade Began Disintegrating Before It Reached The Front Line, 2025
15. The Centre for European Policy Analysis (CEPA), The Elite Ukrainian Brigade Everyone Wants to Join, 2024
16. Huntington’s Disease Association, Military Campaign, 2023.
17. UK Parliament, Written Question UIN 183925, May 2023.
18. Amnesty International, Ukraine Conflict Reports, 2023.
19. HelpAge International, Older People in Crisis Response, 2022.
20. HelpAge International, If Not Now, When? Keeping promises to older people affected by humanitarian crisis, 2021
21. HelpAge International, Older People in Disasters and Humanitarian Crisis: Guidelines for best practice, 2000
22. HelpAge International, Why Older People are Overlooked in Humanitarian Aid, 2023