A parliamentary committee that scrutinises public spending has made scathing comments about the impact of delays in the publication of the government’s defence investment plan (Dip).

The Dip, originally expected last autumn, has been repeatedly postponed amid warnings that the military faces a huge funding gap over the next four years. It is due to be published before a Nato summit early next month.

In a report, the public accounts committee (PAC) said the delay was undermining credibility with the UK’s allies. The chair of the committee of MPs, Geoffrey Clifton-Brown, said: “Those responsible may argue there are good reasons for the Dip’s continuing absence, but our report makes clear that excuses to the effect of ‘taking the time to get the details right’ simply do not cut it.

“Whatever the content of the Dip when it eventually does appear, the damage from its absence has been done – to the nation’s credibility, to its safety, to its armed forces, and to certainty within its entire defence industrial base.

“Any government minister attempting to explain away this delay to the Dip should instead ask themselves what message the bureaucratic drift of the past months has given to the public, as well as the UK’s allies and its adversaries, and simply apologise.”

The Ministry of Defence (MoD) “has not yet decided which capabilities, infrastructure and people it requires to transform the armed forces to be warfighting-ready within the budget available” and “nor has it secured the cross-government agreement that the plan needs”, the report added.

The UK prime minister, Keir Starmer, has said the plan, originally promised in autumn 2025, will be published before the Nato summit in Turkey, beginning on 7 July.

A spokesperson for the MoD said the government is providing a “generational increase” in defence spending, with an extra £270bn across this parliament.

“The defence investment plan will fix the outdated, overcommitted and underfunded programme we inherited,” said the spokesperson. “We are working hard to finalise it. As the defence secretary told parliament this week, the prime minister is determined to publish it before the Nato summit.”

The PAC report comes as it emerged the MoD is developing a submarine maintenance recovery plan amid reports the Royal Navy’s entire available fleet of hunter-killer submarines is docked.

The Mail on Sunday reported all five Astute-class submarines – which are used to protect the Vanguard submarines that carry nuclear Trident missiles – are out of service while they undergo maintenance and repair work. The First Sea Lord ordered the plan to be developed which would prevent maintenance overruns and increase capacity to achieve war readiness.

An MoD spokesperson said: “Strengthening and sustaining our submarine capability is a top priority and we are taking decisive action to ensure its long-term resilience.

“The strategic defence review has underscored the critical importance of sustained and targeted investment across the defence nuclear enterprise, and we are unwavering in our efforts to deliver the resources, infrastructure and support necessary to meet current and future operational demands.

“We do not routinely comment about specific submarine operations and availability, but British waters are always protected with a range of assets including warships, patrol aircraft and submarines.”

The Mail quoted a naval source claiming that “a lack of investment for decades in providing the backup infrastructure to keep them [submarines] safe” had contributed to the problem.

On Saturday it emerged that a technical issue had been discovered on a UK navy flagship while docked in Norway. The problem with HMS Prince of Wales – one of Britain’s two flagship aircraft carriers built for £6.4bn – was identified during its latest stop in Stavanger, a city in south-west Norway.