Prime Minister Keir Starmer unveiled his long-delayed Defence Investment Plan on Tuesday, promising an increase of £15 billion in funding to better equip Britain to fight the wars of the future in a blueprint he described as his legacy.

In what is most likely his last major policy announcement, Starmer said the plan had been sharpened and went further than a previous document that prompted his ally, John Healey, to resign as defence minister earlier this month, accusing him of failing to secure enough money to keep the country safe.

Starmer will take his plan — which foresees spending of nearly £80 billion a year by 2029 — to Ankara for a NATO meeting on July 7 to 8, where he will want to signal that Britain was on the path to meet its commitment to reach defence spending of 3.5% of GDP by 2035.

But with his expected successor, Andy Burnham, due to take power as soon as July 20, he acknowledged that new governments could "build" on his blueprint.

Some critics said the plan, delayed for more than nine months, was too little, too late.

Plan 'will strengthen Britain's defence'

"When the world is arming and aggression is rising, the best way to avoid war is to prepare for it, the best way to defend is to deter — to have the strength to make your adversaries to think again before they act," Starmer told an audience at a defence company in southern England.

"That is what we are delivering."

After last-minute discussions between the finance ministry and Britain's new defence minister, Dan Jarvis, Starmer said his blueprint would offer funding of £5 billion for investment in drones and autonomous weapons, create a hybrid Navy and make the army more lethal.

It would also strengthen Britain's nuclear deterrent and bolster a programme to build a next-generation stealth fighter jet for the Royal Air Force, Starmer said, adding that would create jobs and boost growth.

Matt Roberts, national officer of the GMB trade union, welcomed the plan, saying it offered "some stability for a sector besieged by insecurity".

"The challenge now is delivery — workers will judge this plan on real jobs, real investment, and real outcomes."

But hours before the plan was published in full, critics already said it was not large enough to make Britain war-ready, especially when military officials have warned that Russia could attack a NATO country as soon as 2030.

General Richard Barrons, formerly commander of the Joint Forces Command, said, while the plan represented progress, Britain would still be left exposed.

"It is still not going to crack the issue of, in order to defend the UK sufficiently well, sufficiently quickly, more has to be done sooner, and that requires more money than is currently on the table," he told BBC Radio.

Defence chiefs have said there is a £28 billion funding gap over the next four years and, with the £15 billion uplift falling short of the total, Barrons said some equipment would not be bought or would be delayed, and corners would be cut on training, infrastructure maintenance and logistics.

But the prime minister defended the plan's costings, saying the settlement was the right choice for the country. He said much of the additional spending would come from reallocating spending from different departments.

"Some capital projects, for example, on roads and energy, which are important but not immediately vital, will no longer go ahead as planned, but this is about taking the necessary choices, the right choices to protect our nation," he said.

"This plan represents our best judgment for what the country needs to meet this moment, and it is a platform on which I know my successor will build."