The Archbishop of Canterbury and Cardinal Vincent Nichols are among leaders paying tribute to Conservative MP Sir David Amess after he was stabbed to death inside a church while meeting constituents.
Cardinal Nichols said he was "shocked and saddened" by the MP's death, which happened during a local constituency surgery at Belfairs Methodist Church in Leigh-on-Sea, Essex.
The cardinal said he was praying for Sir David's family and constituents.
"This death throws a sharp light onto the fact that our Members of Parliament are servants of the people, available to people in their need, especially in their constituencies," he said.
"This horrific attack, as David was undertaking his constituency surgery, is an attack on our democratic process and traditions.
"David carried out his vocation as a Catholic in public life with generosity and integrity. He served in Parliament for four decades and was respected by all political parties across the House. His untimely death is a great loss."
Archbishop Justin Welby said he was "truly devastated" by Sir David's death.
He said the MP's "deep faith fuelled his sense of justice" and that Britain was "all the poorer" for his "untimely" death.
"The murder of an MP, in the course of caring for their constituents, is a deep blow to this country, its citizens and everyone who desires a peaceful and flourishing democracy," he said.
"The only antidote to violence and hatred is love and unity," he continued. "In this horrific and tragic moment we must come together, across political difference, and be the light that refuses to be cowed by darkness."
The Archbishop of York, Stephen Cottrell, said in a statement: "I had the great honour of calling David Amess a friend when I was Bishop of Chelmsford.
"He was the MP for the constituency where I grew up, and not only did he always faithfully serve those people and that place, but had a particular concern for the Christian community born of his own deeply held Christian faith as a member of the Roman Catholic community.
"It is shocking that someone so dedicated to his community and public service was the victim of such violence as he went about his elected duty.
"It is hard to make sense of the horror of what has happened this afternoon but he and his family and those he loves are in my prayers."
Sir David had been MP for Southend West since 1997, and prior to that, Basildon. A 25-year-old man has been arrested on suspicion of murder.
He was 69 and was married with five children.
Prime Minister Boris Johnson praised him as "one of the kindest" people in politics with an "outstanding record of passing laws to help the most vulnerable".
"David was a man who believed passionately in this country and in its future. We've lost today a fine public servant and a much-loved friend and colleague," he said.
Health Secretary Sajid Javid said he was "devastated" by the death of "a great man, a great friend, and a great MP".
"Let us remember him and what he did with his life," he said.
Andy Flannagan, Executive Director of Christians in Politics, said, "There are moments that hold up a mirror to the reality of who we are as a society. This tragic killing of another public servant may well be one of those.
"Are we again exposed to the extreme version of the lazy antipathy that so many of us indulge towards those who answer the call to public leadership?"
Catherine Robinson, spokesperson for Right To Life UK, said the campaign group was grieving the loss of a "pro-life champion".
"Sir David's death is a senseless tragedy and he will be truly missed. Our thoughts and prayers are with his wife Julia and their five children," she said.
"We have had the honour of working with Sir David over the years across a number of issues and he was a passionate and dedicated patron of our charity.
"Sir David was a pro-life champion. Since he was elected in 1983, he always, where possible, used his position as an MP to stand up for the vulnerable, including championing initiatives to introduce more protections for unborn babies and more support for women facing crisis pregnancies.
"Everyone who worked with Sir David knew him to be a kind, caring and jovial man, who showed real care for the most vulnerable in our society".
