If British forces were at war with Russia they would run out of ammunition in "two weeks", according to the Chair of the Defence Committee.
Talking to Forces News, Tobias Ellwood MP said that the UK has gifted so much equipment to Ukraine that it would have a "shortfall" of its own, if it was to tackle Russia itself.
"The amount of ammunition that Ukraine is expending, if we went to war, we'd run out in two weeks," Mr Ellwood said.
Mr Ellwood spoke to Forces News as the Commons Defence Committee published a report calling for military plans under 2021's Integrated Review to be redrawn following Russia's invasion of Ukraine.
He said the world is a "very different" place to a year ago when the Integrated Review was published.
Watch: World looks 'very different' since defence review was published, Mr Ellwood says.
Mr Ellwood noted that in comparison to the 4% defence budget of the Cold War, the current defence spending aim of 2.5% of GDP is "too small, it is a peacetime budget".
The Defence Committee chair said in 'The Integrated Review, Defence in a Competitive Age and the Defence and Security Industrial Strategy' report that "in these uncertain times, our capabilities and readiness must be ironclad.
"With open war raging in Europe, widespread economic instability and the catastrophic Afghanistan withdrawal underscoring the Government's lack of preparedness for international crises, we must be clear-eyed about the challenges ahead."
He added: "It is clear that now is not the time for personnel cuts or budget shortfalls in our Armed Forces."
An MOD spokesperson said: "The Command Paper and Integrated Review put a threat-led approach firmly at the heart of the Ministry of Defence's work.
"We are delivering our vision to support and equip our Armed Forces, including the need to invest for the long term in vital capabilities such as future fighter jets, nuclear submarines and more advanced tanks. This is bolstered by the £24bn settlement over four years.
"We are proud of our personnel and the work they do across the world, including the withdrawal from Afghanistan and our ongoing support for Ukraine.
"We are acutely aware that our nation's resilience is crucial and we will continue to adapt our strategy and response to meet emerging threats and challenges," the spokesperson added.