By William Schomberg and Paul Sandle
LONDON (Reuters) - The campaign to keep Britain in the European Union regained its lead in two opinion polls published on Saturday, giving a boost to Prime Minister David Cameron who is battling to avoid a historic "Out" vote in Thursday's referendum.
A third poll also showed a change in momentum in favor of the "In" camp and Cameron got the backing of a leading newspaper when the right-leaning Mail on Sunday urged its readers to vote to remain in the EU.
"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.
Financial markets around the world are on edge ahead of the June 23 referendum. Recent polls showing the "Out" camp in the lead have weakened sterling and helped wipe billions of pounds off stock markets as investors worried not only about the hit to Britain's economy and its trading partners, but also about the implications of a so-called Brexit for the EU's future.
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 a British lawmaker on Thursday which led to the suspension of referendum campaigning.
Instead, the bounce in support for "In" was more a reflection of growing concerns among voters about the economic impact of a so-called Brexit, it said.
Cameron and his finance minister, George Osborne, have tried repeatedly to focus voters on the economic risks of leaving the EU's single market, pointing to forecasts of a hit from the International Monetary Fund, the Bank of England and most private economists.
CAMPAIGNING SET TO RESUME
Another YouGov poll reported on Saturday but based on surveys conducted on Wednesday and Thursday showed the lead of the "Out" campaign had narrowed to two points from as wide as seven points less than a week ago.
A third poll on Saturday, by polling firm Survation, gave the "In" campaign a three-point lead, reversing a similar lead for "Out" in a Survation poll published as recently as Thursday.
A fourth poll, by Opinium, showed the two camp were running neck and neck with 44 percent support each. That poll was conducted between Tuesday and Friday.
While Cameron got support from the Mail on Sunday's backing of the "In" campaign, its rival The Sunday Times, which sells around half the number of copies as the Mail on Sunday, said it was backing the "Out" campaign.
The Sunday Times urged voters to vote to leave the EU as a way to press for deeper reform which might make the bloc more acceptable for Britain to actually remain in after a second referendum, an idea floated by "Out" campaigner Boris Johnson.
But Cameron told the newspaper that there would no second chance to decide Britain's role in Europe. "This is an irreversible decision with very bad consequences for the British economy," he said in an interview.
Campaigning was due to resume on Sunday after a suspension lasting more than two days following the fatal attack on lawmaker Jo Cox, a member of the opposition Labour Party and a strong supporter of Britain staying in the EU.
The man charged with her murder, Thomas Mair, gave his name as "death to traitors, freedom for Britain" when he appeared in court on Saturday.
(Writing by William Schomberg; editing by Paul Sandle and Cynthia Osterman)