Sir Keir Starmer said he disagrees with Lord George Robertson after the former Nato chief accused the Government of “corrosive complacency” on defence spending.
Lord Robertson of Port Ellen claimed the UK is underprepared for war and ministers are unwilling to make the necessary investment.
The former Labour defence secretary warned “we cannot defend Britain with an ever-expanding welfare budget” in a speech on Tuesday.
Responding to the criticism at Prime Minister’s Questions, Sir Keir said: “Let me start by saying I respect Lord Robertson and I thank him again for carrying out the strategic (defence) review.
“My responsibility is to keep the British people safe, and that is a duty I take seriously. That is why I don’t agree with his comments.
“Last February, that was seven months after taking office, I took the decision to increase defence spending from 2.3% to 2.6%, paid for by my difficult decision on overseas aid.
“Last June, at the Nato summit, I committed to raising core defence spending to 3.5%. Last November, the budget committed record funding to defence. I reaffirm those commitments now.
“The strategic defence review is a 10-year blueprint for national security. The defence investment plan (Dip) will put that into effect. It will be published as soon as possible.”
Lord Robertson had told the Financial Times there was a gap between the Prime Minister’s rhetoric on defence and the action he had delivered, saying Sir Keir was “not willing to make the necessary investment”.
During her clash with the Prime Minister, Conservative leader Kemi Badenoch pressed him on when the Dip will be published, calling for it to come before the end of the parliamentary session.
She said: “Lord Robertson’s criticisms were of the Prime Minister, and he says Britain’s national security is in peril.
“Our armed forces are at the end of their tether waiting for this Government to fund the strategic defence review (SDR).
“There are still two weeks of the parliamentary session left so why won’t the Prime Minister publish the Dip before then?”
Sir Keir did not respond to this directly, instead saying the Government is “spending £270 billion over this Parliament, that’s £5 billion more this year, with defence funding increasing every year”.
The 10-year plan was due to be published in autumn last year to deliver the SDR’s plans.
Mrs Badenoch continued: “Will the Prime Minister put the billions saved from ditching Chagos into defence, or is that going into welfare as well?”
Sir Keir replied that the Government is spending “record amounts on defence,” with the “biggest boost of defence spending since the Cold War”, the “biggest pay rise for our armed forces for over 20 years” and “the biggest investment in military housing for over half a century”.
Defence Secretary John Healey later said he did not agree with Lord Robertson’s assessment.
Answering questions after a meeting of the Ukraine Defence Contact Group, Mr Healey said: “There’s no complacency, and we are getting on with the job in Government, we’re getting on with the job of delivering that strategic defence review, of defending Britain.”
As an example, he pointed to his announcement last week of UK armed forces foiling a Russian covert operation over cables and pipelines in waters north of the UK.
In PMQs, Sir Keir’s defence team also faced criticism from Labour backbenchers, including the Commons Defence Committee chairman Tan Dhesi.
The Slough MP described Lord Robertson’s intervention as “sobering”, and warned delays to the Dip risked causing “further damage” to the defence industrial base.
“His comments align with what the Defence Committee has been highlighting for several months now, that we are ill prepared to face the threats that we as a nation currently are facing in a more volatile world,” Mr Dhesi said.
Emma Lewell, the Labour MP for South Shields, said bolstering defence investment “should not come at the expense of those pensioners and people with disabilities receiving welfare”.
Defence minister Luke Pollard told the Commons “not a day goes by” without a new defence contract being signed, pointing to his visit to Andover, Hampshire, earlier on Wednesday to announce an £879 million, 1,200-job contract for Apache helicopter maintenance.
He also said the Government has £5 billion extra in its budget this year “to address the hollowing out and underfunding” of armed forces which he warned had taken place over recent years.
Conservative shadow defence minister Mark Francois, who summoned Mr Pollard to the despatch box using an urgent question, said: “One Labour peer told me prior to Easter that waiting for the Dip was like Waiting for Godot – except that Godot finally turned up.”
Responding to Mr Francois’ request to name the month and year the Dip would be published, the minister said: “We are working flat out to deliver the Dip, and we will publish it when it is ready.”
Mrs Badenoch had earlier taken aim at Labour MP Samantha Niblett (South Derbyshire), who said she hopes to bring sex toys into Parliament as part of her campaign for more open, inclusive and lifelong sex education.
The Tory leader said: “This is a moment of profound national seriousness, and what are they doing? They’re promoting sex toys in Parliament.
“It gives a whole new meaning to fiddling while Rome burns.”
Downing Street distanced itself from the MP’s “summer of sex” campaign.
Asked if it was appropriate, the Prime Minister’s political spokesman told reporters: “Samantha Niblett is a backbench MP and I’d point any questions to her.”
