The name the police have of the terror suspect arrested on suspicion of murder following the stabbing of a senior Conservative MP is Ali Harbi Ali, Sky News understands.
The 25-year-old, who is a British citizen, with Somali heritage, is not thought to have been previously known to the security services.
However, the investigation into the killing of Sir David Amess is still in its infancy so that could change if new details emerge.
Detectives granted warrant of further detention for man held on suspicion of murdering MP – live updates
The suspect was arrested on Friday at the scene of the attack at a Methodist church in Leigh-on-Sea, Essex, where Sir David, MP for Southend West, had been holding his weekly constituency surgery.
The detained man was previously known to the government’s Prevent scheme, which is a programme to stop radicalisation, a Whitehall source said. This detail was first revealed by the Guardian newspaper, which said that his involvement was short.
Police will be able to keep the suspect in custody until 22 October, after being granted a warrant of further detention by Westminster Magistrate’s Court
The investigation into the attack is being led by Scotland Yard’s Counter Terrorism Policing.
The Met said on Friday that the incident had formally been declared as terrorism by Senior National Coordinator for Counter Terrorism Policing, Deputy Assistant Commissioner Dean Haydon.
Police previously said in the early hours of Saturday that they are not seeking anyone else in connection with Sir David’s death but inquiries are continuing.
Two properties were also being searched in London as part of the investigation, they added.
On Friday, the Duke and Duchess of Cambridge were among those to express “shock and sadness” following Sir David’s death.
Prime Minister Boris Johnson and Labour leader Sir Keir Starmer attended the site of the killing together earlier on Saturday to pay their respects.
The father-of-five had been an MP for 38 years, and while he never held a ministerial role, he was known as someone who took on the causes of his constituents.
He was socially conservative, an early Eurosceptic, and a campaigner for animal rights and against fuel poverty.
Sir David also spent years raising awareness of endometriosis after being approached by a constituent who suffered from the painful condition.
Home Secretary Priti Patel said it is “right and proper” that MPs are accessible to members of the public following Sir David’s killing – and stressed that politicians’ safety and an open democracy “can absolutely be balanced”.
Operation Bridger, a nationwide police protective security operation established in 2016, will reach out to the more than 600 MPs to discuss their security arrangements following the murder of Sir David at a constituency surgery on Friday – with officers then reporting their findings back to Ms Patel.