The 25-year-old man was arrested on suspicion of murder after Sir David, Member of Parliament for Southend West, was fatally stabbed at an address in Eastwood Road North, Leigh-on-Sea, shortly after 12:05hrs on Friday, 15 October.
A knife used in the attack was recovered at the scene. No one else was treated for injuries following the incident.
The incident has been formally declared as terrorism by Senior National Coordinator for Counter Terrorism Policing, Deputy Assistant Commissioner Dean Haydon. The Met’s Counter Terrorism Command is leading the investigation.
Late on Friday, 15 October, whilst in police custody, the man was subsequently further detained under section 41 of the Terrorism Act 2000 and he is now being held at a London police station.
On Saturday, 16 October, detectives were granted a warrant of further detention at Westminster Magistrates’ Court, allowing them to keep the man in custody until Friday, 22 October, when the warrant expires.
As part of the fast-paced investigation, officers have attended three addresses in the London area and conducted searches. One of these searches has concluded and the others are ongoing. A post mortem examination has taken place today.
Detectives would urge any witnesses or anyone with information about this incident to contact police. If you have any information that could assist the investigation, please call police in confidence on 0800 789 321.
Anyone with moving footage or pictures is asked to submit them via the UK Police Image Appeal website.