Andy Burnham will have to find an extra £4.7bn for defence in his first budget, after Keir Starmer announced a £298bn defence investment plan (Dip) without having fully identified how it will be funded. Sources close to the Makerfield MP said he would not try to renegotiate the Dip after the outgoing prime minister announced its details at a press conference on Tuesday. Those close to the likely next prime minister acknowledged he would have to find nearly £5bn more than expected to fund the plans over the next four years, which one Burnham ally likened to an “unexploded bomb”.

The Guardian understands the Makerfield MP was not told about the funding gap when he was briefed on the plan. A defence insider said it was “madness after all that wrangling to have left a £4.7bn black hole for someone else to fix”, while the Conservatives described the plan as a “delayed-action poison pill” for Burnham. Starmer said on Tuesday the long-delayed Dip would make Britain safer by “driving a generational transformation of our armed forces”.

Overall defence spending will rise marginally from 2.6% of GDP in 2027 to 2.7%, or nearly £80bn, by 2030. Starmer said that would put the UK “on a trajectory” to hit 3% in the next parliament, although it remains well below a Nato target of 3.5% by 2035. It counts as a £1.5bn improvement obtained by the new defence secretary, Dan Jarvis, who is fighting to keep his job after Starmer leaves, compared with the £13.5bn offered to John Healey, who resigned in protest at the money he had been offered.

Starmer told a press conference at a drone manufacturer in Berkshire: “It focuses our resources squarely on the readiness of our armed forces, reversing the cuts of recent years, prioritising the availability of our forces and assets, rebuilding ammunition stockpiles, ensuring we are ready to fight and defend our nation and better prepared to win.” The plan, which was due to be published nearly a year ago, puts drones, fighter jets and nuclear weapons at the heart of the country’s military capability. The overall package will cost £298bn over the next four years, £15bn of which was newly announced on Tuesday. It includes: - £47bn on new nuclear submarines, including the Dreadnought replacement for the Trident submarines and the new Aukus attack submarine project, being developed with Australia and the US.

- £13bn on a new nuclear warhead and £1.7bn on nuclear fuels. Another promise to pay £1bn for 12 Lockheed Martin F-35A jets capable of carrying nuclear bombs will come after 2030. - £8.6bn on the development of the Gcap next-generation fighter aircraft in a joint project with Italy and Japan, plus an extra £1.1bn to keep existing Typhoons in service until the 2040s.

- A total of £5bn more on drones, £1bn more than announced in last year’s strategic spending review, with investments in air, land, sea and underwater drones to operating alongside soldiers, warships and fighter jets. It would be partly funded by £10.7bn of efficiency savings within the MoD, including cutting civil servants by 10% and spending on consultants by £1bn. A few military capabilities would be retired early, including 34 Wildcat helicopters used by the army, while the development of Storm Shadow missiles would be halted.