The change is one of several reforms in upcoming legislation that seeks to expand the country's "strategic reserve" pool of veterans and reservists who could be liable to be recalled in a crisis.

Currently, the recall liability for non-officer veterans in the British Army and the Royal Air Force ends either 18 years after discharge or at age 55, whichever comes first.

For Royal Navy or Royal Marines non-officer veterans it is six years after discharge or at age 55, but this will increase to 18 years after discharge to "align" with the two services.

The changes in the Armed Forces Bill introduced to Parliament on Thursday will come into effect from the spring of 2027, the Ministry of Defence said in a statement.

Those who have already left the military will not be affected unless they opt in.

"The Bill expands the reserve pool, allowing the most experienced volunteer reservists to step up and strengthen UK readiness as global threats continue to grow," the MoD posted on X.

The changes will also lower the threshold for reservists to be recalled so that reservists can be recalled for "warlike preparations".

Currently the threshold for mobilisation is a "national danger, great emergency or attack on the UK".

"As the threat to our nation grows, we must ensure our Armed Forces can draw on the numbers and skills required to meet it," Lieutenant General Paul Griffiths, who has been tasked with ensuring the UK is ready for combat, said as part of the MoD statement.

"These reforms will allow us to mobilise that talent rapidly when it matters most, strengthening our readiness and aligning with a similar approach many NATO forces are taking to bolster their own resilience."

Around 95,000 people are estimated to be liable for recall as part of the strategic reserve, the statement said.

The change comes as the UK attempts to boost its military capabilities and the size of its force in the face of growing threats, particularly from Russia.

In December, Britain's armed forces chief, Richard Knighton, issued a call for the country's "sons and daughters" to be "ready to fight" in the face of growing threats, including from Russia.