(Adds McNeilly online post)

LONDON, June 17 (Reuters) - A whistleblower who alleged that Britain's nuclear-armed submarines have major security flaws has left his post in unspecified circumstances, the Royal Navy said on Wednesday, after an inquiry found no safety breaches had occurred.

Able Seaman William McNeilly released a lengthy dossier online last month in which he said the Trident nuclear defence system was vulnerable to its enemies and potentially devastating accidents because of safety failures.

The government held an inquiry into his allegations which concluded many of his assertions were factually incorrect or the result of misunderstandings.

"We can confirm that AB McNeilly has left the Naval Service, the details of which are a matter for the individual and his employer," a spokeswoman for the Royal Navy said in a statement.

McNeilly was initially arrested after failing to report for duty and then confined to military accommodation while being investigated.

In an online post on Wednesday, purportedly written by McNeilly but which could not be independently verified by Reuters, the sailor repeated his concerns about safety and said the Navy had fired him.

"Most people know that I acted in the interest of national security. However, I was still given a dishonourable discharge from the Royal Navy. On the claim that my sole aim was to discredit their public image," the post said.

"It is shocking that some people in a military force can be more concerned about public image, than public safety." (Reporting by Kylie MacLellan; Editing by Andrew Osborn)