AN investigation into how submarine documents came to be found in the toilets at Barrow's Wetherspoons has been completed.

The Royal Navy confirmed the papers found were generic training documents and did not contain any classified information.

Files about the £1.3bn Barrow-built 'hunter killer'  HMS Anson had been left in the loos at The Furness Railway in April last year.

The documents appeared to show the inner workings of the submarine and had been used by submariners who were training in how to isolate and depressurise elements of its system, according to reports.

A source told The Sun newspaper the pub was packed when the files, marked 'official sensitive', were discovered on the floor of a cubicle on a busy Saturday night.

An investigation into the incident was completed by the Royal Navy.

It confirmed action had been taken but has remained tight-lipped about what that entailed, amid security sensitivities.

A Royal Navy spokesperson said: “These were generic training documents that carry no classified information.

"This matter was investigated fully at the time and appropriate action was taken.”

HMS Anson is the fifth of the new Astute-class attack submarines to join the Royal Navy fleet.

The vessels are capable of firing tomahawk missiles and described as the 'largest, most advanced and most powerful attack submarines' ever used in the navy on its website.

Government guidance says ­that information marked as 'Sensitive' should only be shared on a 'genuine need to know' basis and could have damaging ­consequences if lost, stolen or published.

A naval source said at the time of the incident: “These documents enable submariners and contractors to understand how systems interact.

"They do not detail how they work, just that they exist.”

They added that the files only contained simplistic designs of the systems on board, without revealing how they work.

Official sensitive documents are one level below Secret.

A total of seven Astute nuclear submarines are being produced at Barrow's shipyard, with two more left to complete.