With Britain still reeling from the killing of Labour Party MP Jo Cox, the EU referendum campaigns got back underway on Sunday with only four days left until a crucial vote that will determine whether the UK will remain in or leave the EU.

In the wake of Cox's killing on Thursday, both the "Remain" and "Leave" camps suspended campaigning for three days. On Saturday, authorities charged 52-year-old Thomas Mair with Cox's murder.

But with polls suggesting the referendum is too close to call, both sides are set to resume campaigning.

Prime Minister David Cameron, who wants Britain to stay in the European Union, said the country was facing "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," Cameron wrote in "The Sunday Telegraph." "If we were to leave and it quickly turned out to be a big mistake, there wouldn't be a way of changing our minds and having another go. This is it."

Luxembourg Foreign Minister Jean Asselborn on Sunday described Cameron's call for a referendum on the UK's future in the EU as a "historic mistake" due to the consequences it may have for other member states.

"It cannot be ruled out that Brexit leads to a domino effect in Eastern Europe," Asselborn told German newspaper "Tagesspiegel am Sonntag."

Newspapers take sides

Meanwhile, Britain's Sunday newspapers picked sides in their final editions before the referendum. Newspapers "The Mail on Sunday" and "The Observer" backed the "Remain" camp, while "The Sunday Times" and "The Sunday Telegraph" broadsheets supported quitting the EU.

The EU "belongs to the past," declared "The Sunday Telegraph." "The Leave campaign has articulated an ambitious vision for Britain as an independent nation, once again free to make its own decisions," it said.

"The Observer" said: "For an international, liberal and open Britain, we need to be part of the EU."

"Outside the EU, our role in the world would be diminished," it added.

Cameron, finance minister George Osborne and opposition Labour leader Jeremy Corbyn, from the "Remain" camp, were all set for major TV appearances on Sunday, while Nigel Farage, leader of the UK Independence Party, was set to do the same for the "Leave" camp.

Polls boost 'Remain'

Meanwhile, the "Remain" campaign regained its lead in two opinion polls published on Saturday

A YouGov poll for "The Sunday Times" newspaper showed support for Britain staying in the EU had restored a narrow 44-43 percent lead over the "Out" campaign.

That poll was based on interviews conducted on Thursday and Friday, but "The Sunday Times" said the shift did not reflect the fatal attack on Jo Cox. Instead, the bounce in support for "In" reflected growing concerns among voters about the economic impact of a so-called Brexit, it said.

In a second poll published on Saturday by polling firm Survation, the "In" campaign had a three-point lead, reversing a similar lead for "Out" in a Survation poll published as recently as Thursday.

"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," said Anthony Wells, a polling director with YouGov.

Cameron said the British economy "hangs in the balance," with trade and investment set to suffer in the event of a "Leave" vote and a "probable recession" that would leave the UK "permanently poorer."

ls,bw/jlw (AFP, Reuters)