Britain hasn’t got enough troops to deploy a large force into Ukraine for long, Sir Keir Starmer has been warned.

The Prime Minister has said he is “ready and willing” to send soldiers to the frontline if a peace deal is brokered to end the Russian invasion of Ukraine.

But a former head of the British Army, Lord Dannatt, warned “we haven’t got the numbers and we haven’t got the equipment to put a large force onto the ground for an extended period of time.”

Health Secretary Wes Streeting said it is “premature” to talk about how many British troops could be sent to Ukraine.

Asked for his reaction to the Prime Minister’s comments in the Daily Telegraph, Lord Dannatt said: “My reaction is the Prime Minister is doing the right thing. But, of course, doing the right thing comes at a price.

“If the Prime Minister is serious about wanting to deploy British troops, put boots on the ground in Ukraine as part of a peacekeeping force, he’s got to realise that’s going to come at a considerable cost.”

Lord Dannatt later went on: “Frankly, we haven’t got the numbers and we haven’t got the equipment to put a large force onto the ground for an extended period of time at the present moment.

“Now, if Keir Starmer wants to do that, that’s fine. The British Army will always stand up to the plate, but here we go again. We’ve got to have the right number of people with the right equipment and the right training, and start to fund that now.”

Defence chiefs on Friday urged Sir Keir to give soldiers a “national arsenal” of drones and uncrewed ground vessels.

Military chiefs told the Prime Minister what they need to fight the next war, sources said.

A senior Army source told The Telegraph: “A national arsenal, in the form of contracts for goods and services, is needed to realise ambitions about doubling fighting power.

“In simple terms, where today the majority of our lethality comes from crewed and high sophistication platforms, like a tank or an attack helicopter, in the future we want to shift more of our lethality coming from low sophistication and uncrewed systems.”

The source said scaling up production lines in this new sector would put the UK ahead of its adversaries and keep the nation safe.

“Mobilising market power alongside improving our fighting power is how to deal with authoritarian states,” said the Army source.

“The markets will do more than the missiles will ever do to make them think twice about starting a war with us. We get to be the first movers if we invest.”

Health Secretary Wes Streeting told Times Radio: “The Prime Minister will be travelling to France to meet with other European Nato leaders to discuss what is a once-in-a-generation moment for the collective security of our continent, which isn’t just about the future of Ukraine

“That’s why the gathering today is important. Next week, he’ll be travelling to Washington to meet with President Trump, no doubt relaying the outcome of some of those discussions today.”

Asked what the scale of a potential peacekeeping force could be and if the Government would be prepared to carry out a recruitment drive, he said: “I think it’s premature to be talking about numbers.”

Asked if the pressure was on to go beyond 2.5%, he said: “Well, as I say, we came into government with a clear commitment to get up to 2.5% and we’re having to do that alongside grappling with a wide range of challenges.

“That’s why sometimes we’re having to say no when people are going coming along with some very worthy things for investment and saying, ‘I’m sorry, but we can’t afford to do that right now’.”

He did not answer the question of whether that meant saying no to lifting defence spending to 3% or 3.5%.

He reiterated plans to be “on a path to 2.5%” when asked if spending 2.5% of GDP on defence was the limit or if the Government could go higher.