Former London Mayor Boris Johnson speaks as Michael Gove listens at a Vote Leave rally in London, Britain, June 19, 2016.
Former London Mayor Boris Johnson speaks as Michael Gove listens at a Vote Leave rally in London, Britain, June 19, 2016.

LONDON - The campaign to decide Britain's membership of the European Union restarted on Sunday after a three-day hiatus following the killing of lawmaker Jo Cox, with Prime Minister David Cameron warning Britons they faced an "existential choice" on Thursday.

Campaigning activities ahead of the June 23 EU referendum resumed with two opinion polls showing the 'Remain' camp recovering some momentum, although the overall picture remained one of an evenly split electorate.

With five days left until the ballot, the rival campaigns returned with a raft of interviews and articles in Sunday's newspapers, covering the familiar immigration versus economy debate that has defined the campaign so far.

British Prime Minister David Cameron delivers a sp
FILE - British Prime Minister David Cameron delivers a speech to supporters of the "Stronger In" campaign event in Witney, Oxfordshire, England, May 14, 2016.

Cameron, who leads the campaign to stay in the EU, urged voters to consider the economic impact that leaving the 28-member bloc would have.

"We face an existential choice on Thursday," he wrote in the Sunday Telegraph. "So ask yourself: have I really heard anything - anything at all - to convince me that leaving would be the best thing for the economic security of my family?"

Michael Gove, a senior spokesman for the rival "Leave" campaign, said leaving would actually improve Britain's economic position.

"I can't foretell the future but I don't believe that the act of leaving the European Union would make our economic position worse, I think it would make it better," he said in an interview with the same newspaper.

Both men praised Labor Party lawmaker Cox, an ardent supporter of EU membership, who was shot and stabbed in the street in her electoral district in northern England on Thursday. A 52-year-old man appeared in a London magistrate's court on Saturday, charged with her murder.

"Leave" campaigner Nigel Farage, leader of the UK Independence party (UKIP), appeared to indicate he thought Cox's killing had had an adverse effect on the "Out" campaign.

"It has an impact on the campaign for everybody," he told ITV's Peston on Sunday show when asked whether it would affect the referendum outcome. "We did have momentum until this terrible tragedy."

The only opinion poll carried out since the killing showed support for "In" at 45 percent ahead of "Out" on 42 percent — a reversal of the three-point lead that the pollster, Survation, showed for 'Out' in a poll conducted on Wednesday.

Two other polls published on Saturday showed the "Remain" campaign had regained its lead over "Leave," while another showed the two camps running neck and neck.

But pollsters said most of these surveys were carried out before Thursday's attack, and thus did not reflect the full impact of the event.

"We are now in the final week of the referendum campaign and the swing back towards the status quo appears to be in full force," Anthony Wells, a director with polling firm YouGov, said.

'Disgusting and vile'

The murder of Cox, a 41-year-old mother of two young children, has shocked Britain, elicited condolences from leaders around the world and raised questions about the tone of campaigning.

"I hope, because of the tragic death of Jo, we can have a less divisive political debate in our country and particularly in the last few days of this referendum," finance minister George Osborne, a leading 'Remain' campaigner, told Peston on Sunday.

Immigration, one of the public's chief concerns ahead of the referendum, has proven to be the most inflammatory issue in the campaign, tapping into fears that EU freedom of movement threatens national security and pressures public services.

But neither side showed signs of backing away from their criticism of each other on the issue.

Osborne called a poster unveiled last week by 'Leave' campaigners showing a line of refugees under the slogan 'Breaking Point' as "disgusting and vile" and reminiscent of literature used in the 1930s.

But Farage, pictured in front of the poster, said the EU had failed to control immigration properly and compromised safety in Europe by allowing in religious extremists who wanted to attack Western states.

"All we have said in this referendum campaign is we want to take back control of our lives, take back control of our borders and put in place a responsible immigration policy," he said, rejecting Osborne's criticism.