Britain's ruling Conservative Party has said it will bring back national service if it wins power again in the UK general election on July 4.

Eighteen-year-olds would either choose to join the military full-time for 12 months or spend one weekend every month volunteering in their community over a year, under the plans announced late Saturday.

Prime Minister Rishi Sunak said the scheme would "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," he said in a statement.

Despite Sunak saying it would be mandatory, his interior minister James Cleverly told Sky News on Sunday that there would be no criminal sanctions for any young person who refuses to take part.

The Conservatives, in power since 2010, estimate the scheme will cost around £2.5 billion ($3.2 billion) a year, with the first teenagers taking part in September 2025.

Young people 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.

Volunteering could include helping local fire, police and NHS services as well as charities tackling loneliness and supporting elderly, isolated people, the party added.

Political commentators viewed the announcement as a headline-grabbing attempt to draw clear dividing lines between the Conservatives and the main opposition Labour Party, which enjoys double-digit leads in opinion polls.

Labour, led by Keir Starmer, branded the announcement an unserious, "desperate" unfunded pledge from a party "bankrupt of ideas".

Britain had national service between 1947 and 1960, with men between the ages of 17 and 21 serving in the armed forces for 18 months.

Several European countries, including Norway and Sweden, have some form of temporary conscription.