Campaigning for Britain's EU referendum resumed today following a pause after the shock murder of MP Jo Cox, with the latest opinion poll average putting the rival camps neck-and-neck.
Prime Minister David Cameron warned there was no "turning back" if Britons vote to leave the European Union, saying it would be a "humiliation" for the nation.
As polls showed the Remain camp gaining ground just four days from Thursday's critical in-or-out vote, leading Brexit campaigner Nigel Farage said Cox's murder had cost the Leave campaign momentum.
Her alleged killer, 52-year-old Thomas Mair, shouted "Death to traitors, freedom for Britain", when he appeared in court yesterday.
Prayers were said for Cox, a 41-year-old mother of two, at a church service Sunday less than a kilometre away from the scene of her murder in the northern English village of Birstall.
Cox, an active Remain campaigner, was stabbed and shot on Thursday in an attack that shocked the country, the first murder of a sitting British lawmaker since 1990.
"Her humanity was powerful and compelling and we would do well to recognise her as an amazing example: a 21st century Good Samaritan," Reverend Paul Knight said at the church service.
After a three-day pause, political leaders hit the stump again on their final push for votes in a referendum that will shape not only the future of Britain but also the EU.
The What UK Thinks website's average of the last six polls, conducted between June 10 and Saturday, put the Remain and Leave camps level at 50-50, excluding undecided voters.
The Leave camp had been a few percentage points ahead in recent polling, but fresh surveys showing a rise in support for remaining brought the average neck-and-neck.
A Survation poll conducted on Friday and Saturday put Remain at 45 per cent and Leave at 42 per cent -- the reverse of its findings on Thursday.
UK Independence Party (UKIP) leader Farage said Cox's killing had halted Leave's upward trajectory.
"We did have momentum until this terrible tragedy," he told ITV television.
The Sunday Mirror newspaper said there was a "dramatic swing in 'mood'", calling it "The Jo effect", citing its own ComRes polling.
Cameron said Britain was facing an "an existential choice" from which there would be "no turning back".
"If you're not sure, don't take the risk of leaving. If you don't know, don't go," he wrote in The Sunday Telegraph newspaper.
"It would be a one-off and permanent diminution in our standing in the world; an abject and self-imposed humiliation for a proud and important country like ours."
His finance minister George Osborne told ITV television that Britain would be "a lot poorer" outside the EU, saying the economy could shrink by at least five percent to six per cent.
