The Ministry of Defence has censored official warnings about the safety of the Trident nuclear weapons system based on the Clyde, the Sunday Herald can reveal.

Annual reports from the MoD’s internal watchdog, the Defence Nuclear Safety Regulator (DNSR), have been abruptly classified as secret. Published for the last ten years, the reports have repeatedly warned of the dangers of spending cutbacks, staff shortages and accidents.

But now the MoD says that the reports will be kept under wraps in the interests of “national security”. This has prompted a tirade of accusations that it is trying to hide “embarrassing” concerns about nuclear safety, and avoid public scrutiny.

DNSR annual reports since 2006 have been released by the MoD after an early challenge under freedom of information law. They have frequently highlighted the safety risks of a growing shortage of suitably qualified and experienced nuclear engineers.

The report for 2014 warned that the lack of skilled staff was “the principal threat to the delivery of nuclear safety”. It also cautioned that “attention is required to ensure maintenance of adequate safety performance” for ageing nuclear submarines.

Similar concerns were highlighted in DNSR reports for 2013, 2012 and previous years. The 2007 report flagged up 11 "potentially significant risks" at military nuclear sites, and the 2006 report warned that "crew fatigue" could cause hazards during the transport of nuclear warheads by road.

But the latest concerns for 2015 and 2016 have been concealed by the MoD. The entire text of the last two DNSR annual summaries has been redacted from wider reports published by Defence Safety Authority because they “would or would likely impact national security.”

“Nuclear safety has not been compromised,” says a recent note on the MoD’s website. “No further detail or comment will be made on those elements redacted.”

The MoD’s move has been attacked by Fred Dawson, an MoD nuclear expert for 31 years until he retired as head of radiation protection policy in 2009. “The obvious conclusion to draw is that there is something to hide,” he told the Sunday Herald.

He accused the MoD of ditching previous commitments to openness and transparency. “The absence of any part of the reports being placed in the public domain will reduce what little public confidence there is in the MoD’s bland assurances,” he said.

John Large, an independent nuclear engineer who has advised governments, argued that the MoD was currently facing serious logistical, technical and resource problems. “By redacting and excluding anything nuclear, these recent reports reveal the MoD’s contempt and utter disregard for public concerns about nuclear safety,” he said.

The DNSR had withdrawn into the MoD’s “inner sanctum of secrecy”, he warned. “These reports attempt to airbrush out the facts by turning a blind eye.”

Large called for the MoD’s nuclear activities to be independently regulated by a civilian watchdog. “In operating and maintaining its nuclear systems the MoD is not at all accountable to independent scrutiny and regulation,” he said.

According to Dr Phil Johnstone, who has been researching nuclear issues at the University of Sussex, there were “serious concerns” about sustaining skills for the defence nuclear programme. “Has the situation now become so embarrassing that this year it cannot be disclosed?” he asked.

His colleague at Sussex University, professor Andy Stirling, added: “If national security is used as an excuse for concealing uncomfortable truths about safety, then questions are raised over whether a system supposedly aimed at protecting the UK is becoming more of a threat.”

The SNP’s Westminster defence spokesperson, Stewart McDonald MP, insisted that safety must be paramount at nuclear sites. “Any suggestion that there are concerns because of resource shortages is totally unacceptable,” he said.

“These reports raise yet more questions for the MoD about what it is that needs to be kept secret now after years of increased transparency.”

David Cullen, from the monitoring group, Nuclear Information Service, pointed out that the publication of previous DNSR reports had not caused security problems. “It is totally unacceptable for them to hold it back just because it is embarrassing or inconvenient,” he said. “Without this information parliament and the public cannot hold them to account, which is bad for safety standards.”

The Scottish Campaign for Nuclear Disarmament thought the secrecy was very worrying. “It suggests that there has been a lack of progress on issues which have been raised in previous reports,” said campaign chair, Arthur West.

The MoD maintained that its nuclear programmes were “fully accountable” to ministers and faced regular independent scrutiny. “We recognise there is a legitimate public interest in the safety of this programme, but we would not publish information that could be exploited by potential adversaries, compromising our national security,” said an MoD spokesman.

The withheld information could be used by enemies to undermine the UK’s nuclear capabilities, he warned. “The MoD cannot accept any compromise of our capabilities in the current security climate,” he added.

“Withholding these assessments will not prevent effective management and independent assessment of the defence nuclear programme. Overall, the programme achieves the required standards of nuclear and radiological safety.”

Nuclear safety warnings in previous official reports

2014: shortage of engineers is “the principal threat to the delivery of nuclear safety”

2013: sustainability of the necessary nuclear skill set “remains fragile”

2012: ageing nuclear submarines require attention “to ensure maintenance of adequate safety performance"

2011: "lack of adequate resource to deliver the defence nuclear programmes safely"

2010: risks of accidents getting “progressively worse” because of “painful” spending cutbacks

2009: spending cuts meant that it was no longer possible to ensure that nuclear activities “remain safe”.

2008: some areas “barely resourced” to deliver nuclear safety

2007: 11 "potentially significant risks" at nuclear sites across the UK

2006: "crew fatigue" could cause hazards during the road transport of nuclear weapons

2005: "slow progress in implementing the regulation framework for the nuclear weapons programme”