Britain could not fight Russia for more than two months, the Deputy Chief of Defence staff has admitted.

Lt Gen Sir Rob Magowan said the UK’s Armed Forces would have to manage the “operational risk” that came with not having the resources he would like in future wars.

It comes after Grant Shapps, the Defence Secretary, told MPs he had lobbied Rishi Sunak and Jeremy Hunt for more money to be spent on defence in the recent Budget, but failed to secure an increase.

Appearing before MPs at the Commons defence committee, the senior Royal Marines officer said: “We’ve been very clear that the amount of money we’re spending on munitions at the moment ... which is significant ... does not meet, in all areas, the threats that we face.

“We’ve been clear that we need to spend more money, above the programme of record, on what we call integrated air missile defence.”

When put to him by Mark Francois, the former Armed Forces minister, that the UK “couldn’t fight (Vladimir) Putin for more than a couple of months in a full-on shooting war because we don’t have the ammunition and the reserves of equipment to do it, that’s true, isn’t it?”, Sir Rob acknowledged that was true.

Mr Shapps added that any such conflict would be fought alongside Nato allies who could collectively outgun Russia, rather than by the UK alone.

Mr Shapps said: “For people watching, and hearing that the UK isn’t ready for war exclusively with Russia, it’s important to understand that because we are in Nato and (mutual defence agreement) Article 5 exists, we would never be in that situation.”

‘Increasingly overstretched’

It comes after a damning inquiry by the Commons defence committee found Britain’s “increasingly overstretched” Armed Forces are not ready for a war with Russia.

It found the Government “will never achieve warfighting or strategic readiness” without urgent reforms to reverse a recruitment crisis and would also need to dramatically boost Britain’s stockpile of weapons and ammunition.

In a stark report, the MPs said that the Armed Forces required more funding to “engage in operations whilst also developing warfighting readiness” or it would have to reduce the “operational burden” on the military.

The committee was told by former defence chiefs that the Armed Forces had been “hollowed out” since 2010 and, “in a peer-on-peer conflict... would have exhausted their capabilities after the first couple of months of the engagement.”

Sir Rob also insisted the UK was “ready for war” although he acknowledged it was not prepared for an enduring war against Russia.

Mr Shapps also told MPs that lessons learnt from the war in Ukraine showed the importance of drone warfare due to the fact they are “lethal” but inexpensive.

“This [Ukraine] is probably the first true drone war and I don’t think we will ever see a war again that doesn’t heavily involve drones,” he said.

Last month, the UK announced it would co-lead with Latvia a new coalition to deliver thousands of kamikaze drones to Ukraine amid mounting ammunition shortages on the front lines.

As part of the scheme Western manufacturers will be brought in to produce first person-view (FPV) attack drones, which Ukrainian military commanders have hailed for changing the landscape of their war with Russia.

Mr Shapps said: “Drones bely the usual facts of war. Usually, every generation gets more expensive to have lethal effect, but actually drones, which sometimes cost a few thousand pounds, can be extremely lethal.”

However, he cautioned that “basic warfare and ammunition” remained important in any future battlespace.