A 75-year-old man killed in the Westminster attack has been named by police as Leslie Rhodes.
Mr Rhodes, from Streatham in south London, was hit by a car. The fourth victim was PC Keith Palmer, who was stabbed to death outside Parliament.
Police said two more “significant arrests” have been made in connection with Wednesday’s incident.
Scotland Yard’s top anti-terror officer Mark Rowley said 50 people were injured and two are still critical.