An opinion poll released on Saturday gave supporters of British EU membership a narrow lead over opponents, a day after another survey had the "Leave" campaign 10 points ahead, underlining how contradictory polling for the June 23 referendum has been.
The pound weakened by as much as 1.2 percent against the dollar immediately after the ORB poll for the Independent newspaper was published on Friday evening.
Betting odds on a British vote to exit the EU also shortened after the survey, conducted on June 8 and 9, put the "Leave" camp 10 points ahead of "Remain", the latest in a run of polls to show rising support for a British exit from the EU.
But a survey by Opinium for the Observer newspaper, conducted between June 7 and 10 and published on Saturday, suggested 44 percent of Britons back continued membership of the bloc with 42 percent against and 13 percent undecided.
Both camps rose 1 percent compared to last week's poll, which was re-weighted to reduce the impact of a disproportionate number of socially conservative voters.
Britons will vote in a June 23 referendum on whether to leave the world's largest free trading area, a decision with far-reaching implications for politics, the economy, trade, defense and migration in Britain and the rest of the EU.
Contradictory opinion polls and a failure to predict last year's outright election victory for Prime Minister David Cameron's Conservatives have led financial markets to pay close attention to bookmakers' odds.
On Saturday, bookmaker Betfair cut the odds of a vote to stay, after the ORB poll, giving a probability of 70 percent, down from 78 percent earlier this week.
Bookmaker Ladbrokes said the ORB poll had caused it to shorten its odds on Brexit to 9/4 from 11/4 previously, implying a rise in the likelihood of a "Leave" vote to 30 percent from 27 percent.
"We thought the Brexit rally was finished, but the 'Leave' odds have tumbled again on the back of the eye-catching 10-point poll," said a Ladbrokes spokesman.
"Polling is a snapshot of voter intention at any given point; a betting market is a predictions market."
Friday's survey gave the "Brexit" camp their biggest lead since the poll series started a year ago, the Independent said. But the official Vote Leave campaign reacted cautiously, tweeting: "We don't believe the ORB online poll, our data suggests it's closer to 50-50."
The mixed picture has heightened market jitters about the outcome, with sterling repeatedly reacting to poll results.
Separately on Saturday, a group of Britain's most eminent scientists endorsed the "Remain" campaign for the UK to remain in the EU, saying that leaving could damage research.
By: James Davey and Costas Pitas (Reuters, London).
Additional Reporting: Guy Faulconbridge and Bill Schomberg.
Editing: Kevin Liffey.
Photo: Pound Sterling Live.
Review: Emerging Market Formulations &
Research Unit, FLAGSHIP RECORDS.
For The #FacebookTeam