Ex-MI5 officer David Shayler was released from Ford open prison, near Arundel, today, vowing to clear his name.
Shayler has been given early release after being jailed for breaching the Official Secrets Act.
The renegade spy, 36, who has served less than seven weeks in jail, will spend another seven weeks electronically tagged and will have to observe a curfew from 7pm to 7am.
In a statement, he said: "My conviction and imprisonment violated both my right to a fair trial and my right of freedom of expression and I intend to fight on."
An Old Bailey jury found Shayler guilty of three counts of disclosing documents and information to a Sunday newspaper in 1997 in breach of the Official Secrets Act.
Trial judge Mr Justice Moses accused Shayler of "blinkered arrogance" and of breaking undertakings he had given before leaving MI5.
Shayler's girlfriend, Annie Machon, said: "The brevity of the sentence reflects the fact that he isn't a traitor and that he did what he did for the right motives."
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