The Royal Navy conducted an investigation last year into allegations of an inappropriate relationship between a senior naval officer commanding a nuclear-armed submarine and Scottish MP Joani Reid, according to BBC News sources.
Reid, the MP for East Kilbride and Strathaven, voluntarily suspended herself from the Labour Party last month after her husband was arrested on suspicion of spying for China. At the time, she stated she was not under police investigation and had done nothing wrong.
The naval officer, who was in charge of a nuclear submarine based at Faslane on Scotland's Gare Loch, faced scrutiny over the alleged relationship with Reid. Following the investigation, the officer was not subject to disciplinary action and was not found to have violated military regulations.
"The security of the nuclear deterrent is our highest priority, and we have robust processes in place to protect the security of our people and capabilities," a Royal Navy spokesperson said. "We will not comment on individual cases."
Security checks were also performed in response to the allegations, with the Ministry of Defence reportedly satisfied with the outcomes. The officer is no longer commanding a nuclear submarine, though this change is understood to be unrelated to the investigation, and he remains in the Navy.
Faslane naval base, located about 25 miles northwest of Glasgow, serves as the home port for all of the Royal Navy's nuclear submarines, including the four Vanguard-class vessels that carry Trident nuclear missiles.
Reid's husband, David Taylor, was one of three political advisers released on bail last month after being accused of assisting a foreign intelligence service. Reid is now sitting as an independent in the House of Commons while the Labour Party conducts its internal investigation.
BBC News has reached out to Reid for comment on the matter.