A man has been arrested in Birmingham by police investigating the Westminster terror attack, in which four people were killed.
The Met Police said the 30-year-old was being held on suspicion of preparing terrorist acts.
Another man, 58, arrested in Birmingham on Thursday, remains in custody.
Khalid Masood, 52, killed three people when he drove a car into pedestrians on Wednesday. He then fatally stabbed a policeman before police shot him dead.
The entire attack on Westminster Bridge and in the grounds of Parliament was over within 82 seconds.
The latest arrest is the 12th to be made by the Met Police in connection with the attack. Nine people have so far been released without charge.
A 32-year-old woman arrested in Manchester remains on police bail until late March.
On Saturday police said they believed Masood acted alone but they were also “determined” to find out whether he had been inspired by terrorist propaganda.
However, Scotland Yard said it was possible they would “never understand why he did this”.
Revelations that Masood’s phone may have connected with messaging app WhatsApp two minutes before he struck have prompted a debate about the responsibilities of messaging services.
Home Secretary Amber Rudd said encrypted messages must be accessible to intelligence services fighting terror, stressing there must be “no place for terrorists to hide”.
She is meeting technology firms this week.
A WhatsApp spokeswoman said the company was “horrified at the attack” and was co-operating with the investigation.
Labour leader Jeremy Corbyn said authorities already had “huge powers”, and a balance was needed between the “right to know” and “the right to privacy”.
All messages sent on WhatsApp have end-to-end encryption, meaning messages are unreadable if they are intercepted by anyone, including the authorities and WhatsApp itself.
So while Masood’s phone is believed to have connected with the app, police may not know what, if anything, was communicated.
Those who died in the attack were: 48-year-old PC Keith Palmer; Aysha Frade, who worked at a college near Westminster Bridge; Kurt Cochran, who was on a trip from the US to celebrate 25 years of marriage; and 75-year-old retired window cleaner Leslie Rhodes.
In a tribute to them at Wembley Stadium on Sunday evening, four wreaths were laid on the pitch by Metropolitan Police Acting Commissioner Craig Mackey, London Mayor Sadiq Khan, FA chairman Greg Clarke and Culture Secretary Karen Bradley.
Fans and players at England’s World Cup qualifier against Lithuania also observed a minute’s silence before kick-off.