All the people arrested in raids following the killing of four people outside Parliament have now been released without charge.
In the immediate aftermath of Adrian Ajao's attack, Scotland Yard raided several properties across the country, including homes in London and Birmingham.
It came as four people lost their lives following his rampage which saw him drive a 4x4 Hyundai into innocent people crossing Westminster Bridge before jumping from the car and stabbing a police officer to death, the Daily Telegraph UK reports.
More than 50 others were injured.
On Saturday the Met said the 12 people arrested in connection with the attack have been released without charge.
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 Ajao, 52, who was shot dead by armed police, 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.