Vigils have been held for Labour MP Jo Cox, who died after being shot and stabbed in the street.
Hundreds of people packed into a church in Birstall, West Yorkshire, on Thursday evening, while a vigil was also held outside Parliament.
Mrs Cox’s husband said the mother-of-two had fought for “a better world”.
Her attacker is reported to have shouted “put Britain first” at least twice. A 52-year-old man, named locally as Tommy Mair, has been arrested.
The attack happened not far from Birstall Library, where Mrs Cox, who was 41, had been holding a constituency surgery on Thursday. She had been the MP for Batley and Spen since last year.
At St Peter’s Church in her home town in the evening, every pew was full as people, including fellow Labour MPs Yvette Cooper and Dan Jarvis, bowed their heads and consoled each other.
The Bishop of Huddersfield, the Rt Rev Dr Jonathan Gibbs, told the service: “She grew up in this community, she lived for this community, she served this community and, in the end, she gave her life for this community.”
Labour leader Jeremy Corbyn was among several MPs to attend an impromptu vigil in Parliament Square in central London.
Mr Corbyn had earlier paid tribute to Mrs Cox, saying the country would be “in shock” and describing the MP as a “much-loved colleague”.
Prime Minister David Cameron said: “The death of Jo Cox is a tragedy. She was a committed and caring MP.” US presidential contender Hillary Clinton has also spoken of a “cruel and terrible assassination”.
Conservative MP Andrew Mitchell, who together with Mrs Cox set up the All Party Parliamentary Working Group on Syria, described her as a “force of nature”.
Writing in the Daily Telegraph, he said she had been a “five foot bundle of Yorkshire grit and determination absolutely committed to helping other people”.
Mrs Cox is the first sitting MP to be killed since 1990, when Ian Gow was the last in a string of politicians to die at the hands of Northern Irish terror groups.
West Yorkshire Police have so far refused to discuss the possible motive behind the killing despite reports that Mr Mair had sympathy for far-right groups.
Political party Britain First, which boasts of its hatred of white left-wing politicians, issued a video statement condemning the attack and said that it had no connection with the incident.
Cafe owner Clarke Rothwell, who witnessed the attack, told BBC News that he had heard Mrs Cox’s attacker say “‘Britain first’ or ‘Put Britain first,’ I can’t say which exactly it was, but definitely ‘Britain first’ was what he said when he was shouting – he shouted it at least twice”.
It has also emerged that a man was cautioned earlier this year after Mrs Cox told police she had received “malicious communications”.
The Metropolitan Police said it was not the same person who had been arrested in Birstall.
Mrs Cox was married to campaigner Brendan Cox, and she had two young children, with the family dividing its time between its constituency home and a river boat on the Thames.
Following his wife’s death, Mr Cox tweeted a picture of his wife standing by the side of the River Thames in London.
He said in a statement: “Jo would have no regrets about her life, she lived every day of it to the full.
“Jo believed in a better world and she fought for it every day of her life with an energy and a zest for life that would exhaust most people.”
Mr Cox vowed to “work against the hate that killed his wife” and added: “Today is the beginning of a new chapter in our lives. More difficult, more painful, less joyful, less full of love.”
Flags are flying at half mast above Downing Street, Buckingham Palace and across Whitehall.
A Buckingham Palace spokesman said the Queen would write privately to Mrs Cox’s husband.