The captain of a British nuclear submarine has stepped down after an investigation into his relationship with Labour MP Joani Reid, whose husband was arrested on suspicion of spying for China. The Royal Navy launched a security probe last year following allegations of an inappropriate relationship between the married officer and Reid, examining potential blackmail risks.

Security checks were conducted this month after Reid's husband David Taylor was arrested under the UK National Security Act. The Ministry of Defence confirmed the checks found no security breach. The officer decided to step back from his position this week for personal reasons after the Financial Times approached the Ministry of Defence about the matter.

Investigators found the captain and Reid exchanged flirtatious messages, though Reid denies this characterization. The pair, who first met as young adults, were in contact after her January visit to the naval base near her constituency. The case highlights ongoing security concerns within Britain's nuclear deterrent program, which relies on four Vanguard-class submarines carrying Trident missiles at an estimated acquisition cost of £23 billion.