The campaign to keep Britain in the European Union has regained its lead in two opinion polls, giving a boost to Prime Minister David Cameron who is battling to avoid a historic "Leave" vote in Thursday's referendum.

Another survey also showed a change in momentum in favour of the "Remain" 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.

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A string of recent polls showing the "Leave" camp in the lead had pushed down on the value of sterling and helped wipe billions of pounds off stock markets.

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

That poll was based on interviews conducted on Friday and Saturday NZT, but the Sunday Times said the shift did not reflect the fatal attack on British MP Jo Cox which has led to the suspension of referendum campaigning.

Instead, the bounce in support for "Remain" was more a reflection of growing concerns among voters about the economic impact of a so-called Brexit, it said.

Another YouGov poll reported today but based on surveys conducted a bit earlier last week showed the lead of the "Leave" campaign narrowing to two points.

A third poll today, by polling firm Survation for the Observer, gave the "Remain" campaign a three-point lead, reversing a similar lead for "Leave" in a Survation poll published as recently as Friday.

But a fourth poll, by Opinium for the Observer, showed the two camps were running neck and neck with 44 per cent support each.

While the Mail on Sunday came out in support of "Remain," the Sunday Times said it was backing the "Leave" campaign.

- Reuters, AAP