A 30-year-old man detained on March 26 in Birmingham on suspicion of preparation of terrorist attacks was released on Saturday, Scotland Yard said.
He was held on March 26, four days after Khalid Masood’s deadly attack which claimed the life of four victims, including police constable Keith Palmer outside the Palace of Westminster.
Eleven other people previously arrested in connection with the investigation have been released without further action.
Inquests into the deaths of both Masood, 52, who was shot dead by armed police after his knife attack on Pc Palmer, and his victims, were opened and adjourned at Westminster Coroner’s Court this week.
Pre-inquest reviews for both cases are expected to be heard at the Royal Courts of Justice on May 19.