The British army could be wiped out in as little as six months if forced to fight a war on the scale of the Ukraine conflict, a defence minister has warned.

Alistair Carns said a rate of casualties similar to that prompted by Russia’s invasion of Ukraine would lead to the army being “expended” within six to 12 months.

He said it illustrated the need to “generate mass rapidly in the event of a crisis”.

Official figures show the army had 109,245 personnel on 1 October, including 25,814 volunteer reservists.

Carns, a former Royal Marines colonel who is also a reservist, said Russia was suffering losses of around 1,500 soldiers, killed or wounded, a day.

“In a war of scale – not a limited intervention, but one similar to Ukraine – our army for example on the current casualty rates would be expended, as part of a broader multinational coalition, in six months to a year,” he added.

In a speech on reserves at the Royal United Services Institute defence think tank in London, Carns, the minister for veterans and people, said: “That doesn’t mean to say we need a bigger army, but it does mean we must be able to generate depth and mass rapidly in the event of a crisis.

“The reserves are critical, absolutely central, to that process.

“Without them we cannot generate mass, we cannot meet the plethora of defence tasks and challenges that we require, and we cannot seamlessly integrate the very best experts into the heart of our armed forces.”

Army reservists serve in their spare time, getting paid to train outside their main jobs.

Carns said the reality of wars such as the one being fought in Ukraine was that they were “attritional in nature”.

He also said the UK needed to “catch up with Nato allies” by placing a greater emphasis on its reserves.

The prime minister’s official spokesman said Defence Secretary John Healey had already spoken about “the state of the armed forces that were inherited from the previous government”.

“It’s why the Budget invested billions of pounds into defence, it’s why we’re undertaking a strategic defence review to ensure that we have the capabilities and the investment needed to defend this country,” they added.

Last month, Deputy Chief of the Defence Staff Lieutenant General Sir Rob Magowan told MPs on the Defence Select Committee: “If the British Army was asked to fight tonight, it would fight tonight.

“I don’t think anybody in this room should be under any illusion that if the Russians invaded eastern Europe tonight, then we would meet them in that fight.”

Earlier on Wednesday, Foreign Secretary David Lammy urged Nato’s European members to step up their defence spending ahead of Donald Trump’s return to the White House.

The US president-elect has accused European countries of relying on American taxpayers for their security.

At a meeting of Nato’s foreign ministers in Brussels, Lammy said “the time to act is now” – although the UK government has yet to set out its own plans for increasing its spending on defence to 2.5% of national output.

He highlighted Russia’s invasion of Ukraine and its involvement in conflicts around the world, including the Middle East.

“In the United Kingdom, we are at 2.3%, heading to 2.5% as soon as we can get there, and we urge all allies across the Nato family to get serious about defence spending.

“All of our populations require us to understand the tremendous security challenges that we are facing at this time,” he added.