Defence Secretary John Healey has been challenged to press the Prime Minister to increase defence spending to 2.5% of GDP if the UK’s threat levels are found to have risen.

The Government’s Strategic Defence Review (SDR) is looking at what reforms are required for the UK to meet threats in the 21st century.

Conservative former minister Sir Iain Duncan Smith said he expects the review to find that the UK is facing the biggest threat since the Cold War as he called for increased defence spending.

Mr Healey said Sir Keir Starmer will “not need any persuading of the arguments and the assessments of the threats” which come from the review, and a pathway to 2.5% will follow it.

The review, being led by former defence secretary and ex-Nato secretary general Lord Robertson, is expected to make recommendations in the first half of 2025.

Responding to an urgent question on when the Government will reach a defence spending target of 2.5% of GDP, Mr Healey told the Commons: “This Government has a cast-iron commitment to spending 2.5% of GDP on defence.

“We promised this in our manifesto at the election, the Prime Minister promised it at Nato in Washington in July, and the Chancellor promised this in the Budget two weeks ago as well as announcing a £3 billion boost for defence spending next year to start to fix the foundations for our armed forces.

“This is on top of £3 billion each year for Ukraine.”

The first duty of any government and this Government is to defend the country and keep our citizens safe

He added: “Everyone agrees that defence spending must increase to match and deal with the threats that we face, and one of our very first acts as a Government was to launch the Strategic Defence Review, which is working at pace to look at the threats we face, the capabilities we need and the resources we have available.

“This isn’t just about how much we spend but it is how we spend it too.”

Mr Healey said the SDR will come first before the Government sets out the pathway to spending 2.5%, adding this will come in the spring.

Sir Iain said: “In China today one shipyard building naval vessels now is outbuilding the whole of the United States’ naval capability. One shipyard, and they have many hundreds.

“So given that, and the threat from Russia, Iran and this totalitarian state axis, could he tell me now, if Lord Robertson comes back and spells out exactly what I believe he will do – which is the biggest threat we face since the Cold War – will he tell the Prime Minister – I say not ‘ask’ but ‘tell’ the Prime Minister: number one responsibility, defence of the realm, 2.5% now?”

Mr Healey replied: “The Prime Minister does not need me to tell him that the duty and the first duty of any government and this Government is to defend the country and keep our citizens safe. And he will not need me, because he commissioned the Strategic Defence Review. My job is to oversee it successfully.

“He will not need any persuading of the arguments and the assessments of the threats and some of the capability recommendations that that Strategic Defence Review, externally led by Lord Robertson, is likely to produce.”

Labour MP Tanmanjeet Singh Dhesi, the chairman of the Defence Committee, said: “We need clarity, we need a timetable, so that not only our allies know where we are heading, but also those within our defence community.”

Mr Healey replied: “It is increasing, it’s increasing with this Government, it increased in the first Budget of this new Government by nearly £3 billion for next year.”

With a former chief of the general staff warning that this country might be directly at war within the lifetime of this parliament

Conservative MP Sir Bernard Jenkin said: “Can I encourage (Mr Healey) that we start telling the truth, that we’re going to have to spend far more than 2.5% of GDP on defence within quite a short number of years?

“With a former chief of the general staff warning that this country might be directly at war within the lifetime of this parliament, can I suggest that he use his friends across this House to influence both his Government and the Treasury influences on our own side, that we’re going to have to bust a gut for a major rearmament programme that we’ve not seen in this country since the 1930s?”

Mr Healey replied: “I know the Treasury will have noted that, they will probably take it as an early representation for the next budget.

“In the meantime, I will ensure that the Strategic Defence Review starts from the point of the threats that we face, war in Europe, conflict in the Middle East, growing threats globally, as well as Russian aggression more widely and beyond Ukraine.

“We will ensure that we are able to match the capabilities we develop with the threats that we face, and we will do so within the resources we have available.”