Civilian staff working on a nuclear submarine reportedly used glue to fix broken bolts in a nuclear reactor chamber.
The repairs to cooling pipes were discovered on HMS Vanguard after a bolt fell off during checks, according to The Sun newspaper.
It was reported that the heads of bolts had sheared off after being over-tightened but, rather than fix the broken shafts, workers for defence firm Babcock allegedly glued the heads of the bolts back on instead.
Reported as a procedural glitch, the details of the alleged gluing of the bolts were reportedly kept quiet, according to the newspaper.
The MOD has not confirmed the use of glue in the fix, however, an MOD spokesperson said "a defect was found from work done in the past when HMS Vanguard was in dry dock".
"It was promptly reported and fixed," they added.
"In light of the issue, the Secretary of State spoke directly with the chief executive office of Babcock to seek assurances about future work."
Babcock, which maintains the UK's fleet of submarines, told the Daily Mail that safety remained its most important priority, adding that its own robust inspection processes discovered the issue and that the company took immediate action to resolve the matter.