More than eight of ten of the incidents took place at HM Naval Base Clyde at Faslane, home to the bulk of the UK’s nuclear submarine fleet.
Scores of safety events were also registered at the Royal Naval Armaments Depot at Coulport, where the nuclear warheads are stored and loaded onto the submarines.
Deidre Brock the SNP MP who obtained the figures, described it as an “appalling safety record” and warned that just one error could subject Scotland to “utter devastation”.
However, defence minister Jeremy Quin said the “safety significance” of the reported events was low, with none causing harm or resulting in the discharge of radioactive waste.
In all, some 443 so-called nuclear site event reports (NSER) took place between 2018 and 2020. Three of the incidents – two at Coulport and one at Faslane – were classed as ‘category B’, the second most severe level on a sliding scale.
The Ministry of Defence (MoD) classifies category B incidents as having “actual or high potential for radioactive release to the environment of quantities below IRR99 [Ionising Radiations Regulations]”.
The figures indicate the frequency of NSERs has increased significantly in recent years. While there were 789 incidents at both sites between 2006 and 2017 – an average of nearly 66 a year – the latest disclosure shows the average now stands at around 148 incidents a year.
Ms Brock, who is the SNP’s environment spokeswoman at Westminster, received the breakdown of NSERs following a written question in Parliament.
She said: “This is an appalling safety record and it just should not be tolerated. Scotland has an arsenal of weapons of mass destruction sitting just a few miles from our biggest city.
“An error on the Clyde could result in utter devastation for Scotland, with enormous numbers of casualties and effects lasting long beyond the lifetimes of anyone living in Scotland today. That makes these ongoing – and increasing – nuclear safety events terrifying.
"It's not just the threat of nuclear explosions though. No-one knows what the aggregate effects of these safety lapses are on the people who work on the bases and the people who live nearby. We don't know, either, what the effects on the environment are – no-one does.”
The figures show there were 378 safety incidents recorded at Faslane, near Helensburgh in Argyll and Bute, over the three-year period, with 65 incidents at Coulport.
A total of 15 incidents – 12 of them at Faslane – were classed as category C, defined by the MoD as having “actual radioactive release to the environment where quantity of release is likely to be below detection threshold”.
A further 100 incidents were deemed ‘category D’, with the lion’s share – some 325 events – classed as ‘below scale’.
Ms Brock. the MP for Edinburgh North and Leith, said there were questions to be asked over the spike in NSERs in recent years.
"The increasing number of these safety incidents is the biggest concern,” she said.
“We haven't seen the predicted increase in employment at the bases, so is it a recruitment problem? Is the MoD struggling to find the specialised personnel to work at Faslane and Coulport?
“The other possibility – that the MoD just isn't taking enough care at the bases – is, hopefully, beyond belief.
"We need rid of these weapons, but it looks like we will have to wait for independence to get that done. In the meantime, though, UK defence ministers must take some fast and effective action to address the safety record.
“They owe that to the people they employ, but they also have a responsibility to safeguard the health and wellbeing of communities and to protect the environment."
The issue has came to the fore during recent Holyrood elections. The SNP’s manifesto maintained its “firm and unequivocal opposition to nuclear weapons” in Scotland, and vowed that Faslane would become a “traditional military and naval base” in an independent Scotland. The Scottish Greens also oppose the housing of nuclear submarines and weapons at Faslane.
Dr Richard Dixon, director of Friends of the Earth Scotland, said: “You would think that our nuclear weapons and submarines would be among the most carefully looked after objects in the whole country, yet there have been hundreds of accidents and mishaps in the last few years and the number of incidents seems to be increasing.
"In at least 18 cases radioactivity was almost certainly released to the environment. Clearly something is very wrong at Faslane and Coulport and this cannot be allowed to continue.
"Unlike any big business, the MoD is allowed to regulate itself, but it is time for the Scottish Parliament to take a good look at the dangers posed by the operations at the two bases.”
In a written answer to Ms Brock on behalf of the UK Government, Mr Quin said: “In line with industry good practice, and in common with other defence and civil nuclear sites, HM Naval Base Clyde has a well-established system for raising NSERs and investigating and categorising them according to their safety significance, whether equipment failures, human error, procedural failings, documentation shortcomings or near-misses.
“The safety significance of all reported events remains low and they are all below level one, the lowest level of the seven-point International Nuclear and Radiological Event Scale.
“None of the events caused harm to the health of any member of staff at the naval base or to any member of the public, and no event resulted in any unauthorised discharge of radioactive waste to the environment.”
A spokesman for the MoD said: “The Royal Navy continues to meet exacting nuclear industry standards. The majority of the incidents listed in the report were low level, but require reporting by the nuclear regulators.
“No harm was caused to any personnel or to the environment.”