A Westcountry-based Royal Navy submariner has admitted meeting two people he thought were Russian secret agents to discuss the movements of British nuclear submarines.
Petty Officer Edward Devenney, 30, pleaded guilty at the Old Bailey yesterday to gathering details of encryption programmes and misconduct in a public office.
He contacted a foreign embassy to try to pass to Russia "crypto material" – computer programmes which are used to encrypt secret information.
Devenney also had information linked to the operation of the now decommissioned Devonport-based nuclear submarine HMS Trafalgar and two other boats in the fleet.
But the two people he eventually met with were not foreign spies but from British secret services.
Devenney appeared at the Old Bailey yesterday and admitted collecting information for a purpose prejudicial to the safety or interests of the state between November 18 last year and March 7 this year.
He denied a second count of communicating information to another person and this will not be pursued by prosecutors.
He will be sentenced on December 12 at the Old Bailey, when parts of the hearing will be held in secret. Mr Justice Saunders told him: "Your sentence will be adjourned to December 12 when I will hear all the matters and consider them all. Until then, you are remanded in custody."
Devenney, who was based at HMS Drake in Plymouth but is originally from Northern Ireland, was arrested by police in the city in March.
It is believed to be the first high-profile spying case to hit the Royal Navy for 40 years. In 1972, a torpedo expert was jailed for 21 years after being caught selling secrets to the Russians.
The case shocked former lieutenant commander Charles Hattersley who spent 12 years on submarines between 1971 and 1983.
"It is axiomatic that the confidentiality and secrecy of communications is upheld to the letter," said Mr Hattersley, now a maritime lawyer.
"For a covert service, if communications are compromised then everything else may be compromised as well. It increases the risk of detection which is exactly what you are striving for."
Mike Critchley, a former naval officer who now publishes Warship World magazine, added: "The main thing is that he has been caught.
"If he had been able to give this information away, you could have had foreign powers reading all our messages between ships and naval headquarters without us knowing it. That's a very serious offence."
A Royal Navy spokesman said: "It would be inappropriate for the service to comment while legal proceedings are ongoing."