The British pound traded near $1.39 for the first time in seven years today.
The cost of hedging against sharp swings also jumped to their highest in more than four years as concerns that Britons could leave the European Union deepened.
The latest poll showed the "in" camp is ahead in a referendum to be held in June but the gap has narrowed.
Support for staying in stood at 51%, while 39% wanted a "Brexit" and 10% were undecided, according to the ComRes poll for the Daily Mail.
Sterling fell to $1.3925 with forecasters now targeting the low of $1.35 seen in 2009.
The currency has come under attack since the start of the week, shedding 3% after several senior members of the ruling Conservative Party threw their weight behind the campaign to leave the European Union over the weekend.
Shortly after 4pm the euro was 0.69% higher at 79.08 pence although the single currency has been held back on worries that the euro zone itself could face a period of uncertainty if Britain chose to leave the Union.
The uncertainty has pushed back chances of an interest rate hike by the Bank of England.
Instead, Bank of England Governor Mark Carney reminded investors that the bank could still use rate cuts and a broadening of a bond-buying programme to boost Britain's economy if needed.
HSBC, a big trader in sterling, said the currency could lose up to 15% of its value and UK economic growth could be up to 1.5 percentage points lower next year if Britons vote to leave the European Union in the referendum.
"A vote for Brexit would have potentially huge consequences for all asset classes. Following a vote to leave we think uncertainty could grip the UK economy, triggering a potential slowdown in growth and a collapse in sterling," HSBC analysts said.