British police on Saturday said the last of 12 people held for questioning over last week's terror attack outside the British parliament has been released.

The 30-year-old man was arrested in Birmingham on March 26 on suspicion of terror acts, part of a larger police action sweeping up a dozen people for questioning.

"All those arrested in connection with the terrorist attack in Westminster on Wednesday, 22 March, have now been released with no further action," Scotland Yard said a statement.

Authorities believe 52-year-old Muslim convert Khalid Masood acted alone when he mowed down crowds with a car on Westminster Bridge, killing three people and wounding dozens more. He then fatally stabbed a policeman at Parliament before being shot dead.

The "Islamic State" group claimed credit for the attack. Counter-terrorism investigators said last week Masood had "an interest in jihad," but have found "no evidence" of a link to IS or al-Qaeda and believe he acted alone.

cw/rc (AFP, AP)