Eighteen year olds would be forced to carry out a form of national service if the Tories are voted back in at the July 4 General Election, Rishi Sunak has announced.

The Prime Minister said Britain has “generations of young people who have not had the opportunities they deserve” as he claimed the policy would help unite society in an “increasingly uncertain world”.

In future, 18-year-olds would be given a choice between a full-time placement in the armed forces for 12 months or spending one weekend a month for a year volunteering in their community, the Tories said.

In an apparent pitch to older voters, the party said this could include helping local fire, police and NHS services as well as charities tackling loneliness and supporting elderly, isolated people.

Opposition critics dismissed the plans as unserious, with Labour saying the pledge would never come to fruition and amounted to “another unfunded commitment”.

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The Prime Minister is seeking to draw a dividing line with Sir Keir Starmer’s party on global security following his pledge to raise defence spending to 2.5% of gross domestic product by 2030.

Heightening his attack on Saturday, Mr Sunak said voters would be left “at risk” with the Labour leader in Number 10 because Britain’s enemies would notice that he “doesn’t have a plan”.

Teenagers who choose to sign up for a placement in the forces would “learn and take part in logistics, cyber security, procurement or civil response operations”, the Tories said.

The Conservatives said they would establish a royal commission bringing in expertise from across the military and civil society to establish the details of what they described as the “bold” national service programme.

The party said this commission would be tasked with bringing forward a proposal for how to ensure the first pilot is open for applications in September 2025.

After that, it would seek to introduce a new “National Service Act” to make the measures compulsory by the end of the next Parliament, the party said.

It estimates the programme will cost £2.5 billion a year by the end of the decade and plans to fund £1 billion through plans to “crack down on tax avoidance and evasion”.

The remaining £1.5 billion will be paid for with money previously used for the UK Shared Prosperity Fund (UKSPF), which is a package to support charities and community groups, the Tories said.

The Prime Minister 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.

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“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.

“This new, mandatory national service will provide life-changing opportunities for our young people, offering them the chance to learn real world skills, do new things and contribute to their community and our country.”

Earlier on Saturday, the PM suggested a government led by Sir Keir would be marked by uncertainty and a “more dangerous world.”

“The consequences of uncertainty are clear. No plan means a more dangerous world. You, your family and our country are all at risk if Labour win,” he said.

Sir Keir’s party pointed out that Lord David Cameron introduced a similar scheme – the National Citizen Service – when he was prime minister.

Lord Cameron’s announcement had no military component to it, instead encouraging youngsters to take part in activities such as outdoor education-style courses as part of his “Big Society” initiative.

A Labour spokesperson said: “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.

“Britain has had enough of the Conservatives, who are bankrupt of ideas, and have no plans to end 14 years of chaos. It’s time to turn the page and rebuild Britain with Labour.”

Liberal Democrat defence spokesperson Richard Foord MP 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.

“This would be far better spent reversing Conservative cuts to troop numbers.”