The 69-year-old, who had been MP since 1983, was seriously injured Friday afternoon while meeting constituents at the Belfair Methodist Church in Leigh-on-Sea, near Southend.
The Meteorological Department said in a statement that Deputy Assistant Commissioner Dean Hayden, Senior National Coordinator of the Counter-Terrorism Police, had formally declared the incident a terrorism.
The investigation is being headed by a counter-terrorism officer.
The force said preliminary investigations have revealed “a possible motivation linked to Islamic extremism”.
25-year-old youth arrested from the spot on charges of murder in police custody Essex Police Station SDR.
Official sources told the PA news agency that the man is believed to be a British national of Somali heritage.
The Meteorological Department said that as part of the investigation, officials are also conducting searches at two addresses in the London area.
The force believes the man acted alone and is not looking for anyone else in connection with the case at this time, but the circumstances of the incident are under investigation.
Essex Police Chief Constable Ben-Julian Harrington said Southend West MP Sir David, 69, was “simply discharging his duties when his life was horrifically cut short”.
Tory veteran Sir David, who was described by Prime Minister Boris Johnson as “one of the kindest, nicest, most gentlemen in politics”, had been MP since 1983 and had five children.
Ms Patel met with police and representatives of security and intelligence agencies after the stabbing, which occurred when Sir David underwent a surgery in his Southend West constituency.
Ms Patel’s spokesperson said, “The Home Secretary has asked all police forces to review the security arrangements for MPs with immediate effect and provide updates at an appropriate time.”
The Daily Telegraph said the review would investigate Operation Bridger, a nationwide police protective security campaign set up in 2016, following several threats to lawmakers following a parliamentary debate on Syria.
Ms. Patel will make a statement in Parliament on the review on Monday, many times informed of.
Sir David was attacked Five and a half years after the assassination of Labor MP Joe Cox An extreme right-wing extremist in his Battelle and Spain constituency in West Yorkshire.
The Speaker of the Commons, Sir Lindsay Hoyle, said police were contacting all MPs to investigate their safety in the wake of Sir David’s murder.
Sir Lindsay told BBC2’s Newsnight: “It’s about doing the right thing with police men across the United Kingdom as it’s about getting involved.”
“I know they are contacting all MPs to check their safety, to reassure them, because in the end we have to make sure that’s a priority.”
He added: “Those who do not share our values or democracy will not win and we will not let them win. We will continue to look at security, this continues and it will continue.”
Sir Lindsay previously said it was correct that security was reviewed after the latest incident, but it was important to avoid “knee-jerk” reactions.
He said on BBC Radio 4’s PM programme: “What we want to do is to ensure that MPs can perform their duties. We have to ensure that MPs stay safe.”
His sentiments were echoed by the father of the House – the longest-serving MP – Sir Peter Botley.
“I predict this weekend, next weekend and across the country in the coming months MPs will hold consultation sessions. That’s what we do,” he told the PA news agency.
“There is no absolute security for anyone. I have always believed that in many other walks of life you are at far greater risk than a Member of Parliament.
“MPs can get extraordinary publicity. We are not extraordinary people. We are normal people trying to act as normal as we can. We accept the risks.
The question is, should MPs stop meeting their constituents face-to-face? The answer is that we will continue to meet our constituents face to face.”
It is not clear at this stage whether the attacker had booked an appointment to see Sir David at his surgery, was waiting for him or had come during the surgery.