The Conservative Party has said it would bring back mandatory national service if it wins the general election.
It said 18-year-olds would have a choice of either joining the military full-time, or volunteering one weekend every month carrying out a community service.
The party is proposing a Royal Commission to consider the details but would plan for the first teenagers to take part in September 2025.
The cost is expected to be around £2.5bn per year.
Under the plans, young people could choose a full-time, 12-month placement in the armed forces or UK cyber defence, learning about logistics, cyber security, procurement or civil response operations.
Their other option would be to volunteer one weekend per month – or 25 days per year – in their community with organisations such as fire, police and the NHS.
Prime Minister Rishi Sunak said he believed bringing back compulsory service across the UK would help foster the “national spirit” that emerged during the pandemic.
Mr Sunak said: “This is a great country but generations of young people have not had the opportunities or experience they deserve and there are forces trying to divide our society in this increasingly uncertain world.
“I have a clear plan to address this and secure our future. I will bring in a new model of National Service to create a shared sense of purpose among our young people and a renewed sense of pride in our country.”
The prime minister said the move would help young people to learn “real world skills, do new things and contribute to their community and our country”.
A Labour Party spokesperson called the announcement “another desperate £2.5 billion unfunded commitment from a Tory Party which already crashed the economy, sending mortgages rocketing, and now they’re spoiling for more.
“This is not a plan – it’s a review which could cost billions and is only needed because the Tories hollowed out the armed forces to their smallest size since Napoleon,” the spokesperson said.
Liberal Democrat defence spokesperson Richard Foord MP accused the Tories of cutting troop numbers.
Mr Foord said: “If the Conservatives were serious about defence, they would reverse their damaging cuts to our world class professional armed forces, instead of decimating them, with swingeing cuts to the number of our regular service personnel.”
“Our armed forces were once the envy of the world. This Conservative government has cut troop numbers and is planning more cuts to the size of the Army.
In the UK, National Service – the country’s old name for conscription – ended in 1960.
The Conservatives said the move would help ensure young people who are unemployed or not in education or training, and those disproportionately represented in the criminal justice system, are diverted away from “lives of unemployment and crime”.
The party said national service would provide “valuable work experience” and “ignite a passion for a future career in healthcare, public service, charity or the armed forces”.
A number of European countries, including Sweden, Norway and Denmark, already have a form of conscription for their armed forces.
Conscription requires young men and women to serve for a limited time in uniform. It means that some of the population will have had some military training – and can then be assigned to reserve units should war break out.
Cuts in the British Army have seen its size fall from more than 100,000 in 2010 to around 73,000 as of January 2024.