The Royal Navy’s new nuclear-powered submarines have been plagued by 69 safety incidents and “near misses” over the last four years.

The Astute class of submarines based at Faslane on the Clyde has seen reported reactor incidents at sea or on shore almost double from 12 in 2014 to 21 in 2015. Though the MoD insists that the incidents are all minor, critics warn that they undermine the boats’ reliability and safety.

The first submarine of the class, HMS Astute, has already been out on operations, and the second, HMS Ambush, was launched in 2011. The third, HMS Artful, was formally handed over to the Royal Navy in December 2015.

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The four remaining Astute submarines are either still being built by the defence firm BAE Systems at its Barrow shipyard, or are due to be built there. The construction programme has been subject to a series of delays and cost overruns.

The Ministry of Defence revealed the number of safety events recorded with Astute submarine reactors between January 2012 and January 2016 in response to a request under freedom of information law. There were an average of more than 17 a year, or one every three weeks.

Reported events are not detailed. But they included “any occurrence that has, or could have, led to a reduction in nuclear or radiation safety or that provides an opportunity for operator experience feedback.”

According to the independent nuclear engineer John Large, the submarines were suffering serious problems. “This continuing experience of the Astute class reactor problems not only imperils the boats when at sea but is likely to result in cutbacks to the number of patrols, voyage durations and the extent of roaming of the high seas,” he said.

John Ainslie, coordinator of the Scottish Campaign for Nuclear Disarmament, pointed out that Astute submarines had been involved in a series of mishaps, including running aground on the Isle of Skye. “It is only a matter of time before one of these incidents results in a serious nuclear accident,” he said.

An MoD spokeswoman said: “In line with our high safety standards, we record all incidents regardless of how minor they are, to ensure lessons are learnt. There are no issues with the safety of the submarines and the MoD has safely operated over 80 nuclear reactor cores since 1963.”