Police arrested five men in their 20s and a 50-year-old man on suspicion of conspiracy to commit murder. All were released on bail and have now been told they will face no further legal action.
Two men, Michael Adebolajo, 28, and Michael Adebowale, 22, will stand trial next month accused of murdering soldier Lee Rigby in Woolwich, southeast London, on May 22.
The pair pleaded not guilty when they appeared at London's Old Bailey court last month by videolink from prison.