British Prime Minister Boris Johnson will lead tributes to David Amess, the veteran lawmaker stabbed to death while meeting constituency voters, as police questioned a man for what they say could have been a terrorist attack.
Amess, 69, was knifed to death at a church on Friday in Leigh-on-Sea, east of London.
At the scene, armed police arrested the 25-year-old son of an ex-media adviser to a former prime minister of Somalia, and he remains in custody.
Amess's killing shocked colleagues and they will gather at parliament later on Monday where usual business will be replaced by a minute's silence and tributes led by Johnson.
There will later be a procession to the nearby St Margaret's Church for a service of remembrance for the father of five.
Amess's family said their hearts had been shattered by such a cruel and violent death.
"Strong and courageous is an appropriate way to describe David. He was a patriot and a man of peace," the family said.
"So, we ask people to set aside their differences and show kindness and love to all. This is the only way forward. Set aside hatred and work towards togetherness."
The murder of Amess, the second British lawmaker to be killed in five years, has prompted questions about politicians' safety and what action should be taken to address the growing problem of online abuse directed at them.
Detectives are quizzing suspect Ali Harbi Ali, a British national, under counter-terrorism laws, looking at a possible motivation linked to Islamist extremism. Officers are also searching properties in and around London.
Ali had been referred to the anti-radicalisation program known as Prevent, the BBC said. But he was not of formal interest to the domestic security agency MI5.
Amess was also chairman of the cross-party committee which looked to foster good ties between Britain and Qatar, and the Times newspaper said detectives were looking at this link. Amess had been on a visit to Qatar last week.
Police have previously warned about the danger the COVID-19 pandemic posed in terms of radicalisation as vulnerable people spent more time online, potentially exposing them to extremist material.
Deputy Prime Minister Dominic Raab said the government was looking at what further measures might be needed to police social media sites and the anonymity granted to users.
Another lawmaker, Chris Bryant from the opposition Labour Party, said he had received a death threat after calling for people to share "a kind message on Twitter today to a politician we disagree with" following Amess's murder.
Police said they had arrested a 76-year-old man on suspicion of malicious communications.
"Let's have nicer language. Let's have our differences, and that's important, ... but what I don't want is the hate and the nastiness," Lindsay Hoyle, the Speaker of parliament's House of Commons, told Sky.
"Today is a starting point where we can change the face of politics."
Australian Associated Press