Britain will spend 3% of GDP on defence by 2034 as Labour accelerates plan after army chiefs issue warning

"In the next Parliament this country will spend three per cent of our GDP on defence," Healey told The Times.

When pressed on whether this was a firm commitment, he said he had "no doubt" Britain would be spending three per cent "in the next Parliament".

The declaration comes just 24 hours after defence sources described the target as still an "ambition".

Healey said there was a "certain decade of rising defence spending" that "allows us to plan for the long term".

The Government's ten-year defence plan, due to be announced on Monday, is understood to be "unaffordable" without the three per cent commitment.

The Office for Budget Responsibility has estimated that reaching three per cent of GDP by the next Parliament would cost the UK an additional £17.3billion in 2029/30.

It remains unclear whether Healey was attempting to bounce the Treasury into approving the spending or if the commitment has been agreed across Whitehall.

One well-placed military source said the review had been delayed because of rows with the Treasury over "discontent that the Ministry of Defence is using it to push for more defence spending".

The commitment would require spending more than £10billion extra on defence annually despite ongoing rows over proposed cuts to public services, including policing and social housing.

Healey has announced an extra £1.5billion investment in military housing to tackle recruitment and retention problems plaguing the armed forces.

The military is losing hundreds of personnel every month, many fed up with being forced to live in dire accommodation.

The investment aims to eradicate mould and damp problems and persuade service personnel to stay.

After meeting a military family at RAF Wittering near Peterborough on Thursday, Healey said: "Our forces make extraordinary sacrifices to serve the country and keep us safe.

"And yet for years, we've forced their families to live in substandard homes. The sorts of homes that you and I just wouldn't want for themselves. That is not good enough. That ends now, with this Government."

Unlike previous defence reviews, Healey chose to focus on housing for personnel rather than gadgets and new kit.

The strategic defence review, delayed from VE Day week, consists of 48,000 words across 130 pages and will be an "transformative" document addressing defence structures.

Troops from American, French and German militaries were embedded inside the UK defence review team to ensure a joined-up approach with Britain's closest allies.

General Sir Roly Walker, the chief of the general staff, warned on Thursday: "The biggest challenge we face is a lack of time."

Speaking at the Royal United Services Institute, he said: "A sense of urgency is needed to face the threats we face and deliver that unfair advantage that our forces in the most dangerous of circumstance to deter and ultimately win."

Military chiefs believe the UK could be just a few years away from war with Russia, yet the armed forces are not equipped to fight, let alone win.