A 30-year-old man has been arrested in Birmingham by officers investigating the Westminster terror attack.

The man was arrested on Sunday on suspicion of preparation of terrorist acts.

He was detained under the Terrorism Act (TACT) and is in police custody.

The man is the 12th person to be arrested in connection with the investigation, with nine others being released with no further action.

Another man, 58, arrested in Birmingham, remains in police custody after a series of raids across the country.

Officers have carried out a total of 15 searches at various addresses in east London, south London, Brighton, Surrey, Carmarthenshire, Birmingham and Manchester.

Fourteen searches have now concluded, with one on-going in Birmingham.

Four people were killed when Islamist extremist Khalid Masood went on an 82-second rampage in Westminster on Wednesday.

Police said they now believe the knifeman acted alone, adding while they were investigating why he carried out the atrocity, that understanding may have died with him.

Met Police announce that terror perpetrator Khalid Masood was born Adrian Russell

Masood drove his car along the bridge at speed, mowing down pedestrians.

He was shot dead by police after he stormed the parliamentary estate on Wednesday afternoon.

Counter-terrorism officers have spent days piecing together what led the 52-year-old to shed his birth name and later unleash carnage on the capital.

On Saturday afternoon officers searched a maisonette in Bredon Croft, Hockley, Birmingham where friends of Masood lived.

A family, who live next door, said Masood used to come wearing Islamic dress and take their neighbours' children to mosque although they did not know where.

One of the mothers at nearby Brookfields Primary School said her daughter was best friends with Masood's, but added: "I always got the chills from him."

Sabrina Hussain described how she changed her mind about taking her child, nine-year-old Skye, to his daughter's birthday party just before Christmas.

Ms Hussain, 28, said: "I thought I was being a bit over-protective, but then I just thought 'no I can't let her go' and we turned the car around and I made up an excuse saying the party had been cancelled.

"I just didn't want her to go.

"There was just something about him that wasn't right."

A childhood friend of the man then known as Adrian Elms told The Sun newspaper he first emerged as a Muslim after serving a jail sentence.

His religious conversion will fuel concerns about the rising threat of criminals being brought under the influence of hardened jihadists while in prison.

Police released specific timings of Masood's murderous spree, showing he took just 30 seconds from mounting the pavement on the bridge to crashing into the perimeter fence at Parliament and fatally stabbing unarmed Pc Keith Palmer.

Masood's victims included US tourist Kurt Cochran and his wife Melissa who were on the last day of a trip celebrating their 25th wedding anniversary.

Mr Cochran was killed and Mrs Cochran was badly injured.

A police officer places flowers and a photo of PC Keith Palmer on Whitehall near the Houses of Parliament (PA)

Aysha Frade, believed to be a 43-year-old married mother of two, also died, along with retired window cleaner Leslie Rhodes.

Dozens of other people were injured in the attack which has prompted acts of tribute and solidarity across the UK and worldwide.

Before England's World Cup qualifier against Lithuania at Wembley Stadium, the mayor of London Sadiq Khan lay a wreath in the centre of the pitch, accompanied by FA chairman Greg Clarke, Acting Metropolitan Police Commissioner Craig Mackey, and Karen Bradley, Secretary of State for Culture, Media and Sport.

The stadium, subject to heightened security, then fell silent for one minute before the 5pm kick-off to remember those who had lost their lives.