British Prime Minister David Cameron struck a familiar note on Sunday, warning voters that the UK economy would suffer if the country became the first member state to leave the European Union.

"I am absolutely convinced that our economy will suffer if we leave," Cameron said during a question and answer session live on BBC television, cautioning that there would be no going back in the event of a Brexit.

Britain would lose free trade access to the 28-member bloc, face higher taxes and budget cuts, the prime minister warned.

He said the UK would be a "quitter" if it opted to leave the EU.

Brexit would send shockwaves across Europe

German Foreign Minister Frank-Walter Steinmeier warned Monday that in the event the UK chose to leave the EU, other member states would have to do everything to prevent the reversal of integration.

"Should the British opt for a withdrawal from the EU, then we cannot continue just doing business as usual with 28 minus one the next day," Steinmeier said in an interview published in local papers.

"We in Europe bear a joint responsibility for ensuring that we do not fall back into a nationalism of single states," he warned.

Both the "remain" and "leave" camps have stuck to familiar themes trying to convince undecided voters just four days ahead of the critical referendum.

For the "remain" camp, the campaign has focused on the economic blowback of leaving the EU.

The campaign for the "leave" movement has largely focused on immigration.

"The debate in this referendum is about our lack of control over economic migration from parts of Europe whose economies are being destroyed by the euro," said Vote Leave chairwoman Gisela Stuart. "This is now affecting families in Britain."

'Leave' campaign losing momentum

An average of the last six polls shows decided voters evenly split. But the murder of pro-EU and Labour Party lawmaker Jo Cox on Thursday appears to have reversed the "leave" camp's recent momentum.

Thomas Mair, the alleged killer, appeared in court on Saturday and shouted: "Death to traitors, freedom for Britain." He has been charged with murder and will undergo psychiatric evaluation.

The only poll carried out since Cox's murder had "in" at 45 percent compared to "out" at 42 percent. Pollster Survation's results showed a reversal for "out," which had a 3 point lead on Wednesday.

"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, told the Reuters news agency.

UK Independence Party (UKIP) leader Nigel Farage said Sunday that Cox's murder had hurt the "leave" 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."

cw/cmk (AFP, Reuters)