The currency initially slipped against the dollar and euro, only to start recovering in mid-afternoon trading.
Meanwhile, the "volatility index" - a measure of investors' uncertainty - has hit levels last seen in the 2008 financial crisis.
The Leave campaign argues that the pound simply retreated to March levels.
Earlier, sterling weakened to a three-year low against the Japanese yen of 149.50. The pound also sank to an eight-week low against the dollar but subsequently recovered to trade 0.14% up at $1.4275. Against the euro, sterling was off intra-day lows, but still down 0.26% at 1.2647.
Investors are spooked by data showing the chances of a Remain vote have fallen, although markets have also been rattled by global economic worries.
With 10 days to go before the referendum vote, two polls at the weekend put the Leave camp ahead, while betting firm Betfair said the implied probability of a vote to Remain has now fallen to 68.5% from almost 80% a week earlier.
"We expect incoming polls to move the pound more aggressively than before," said Charalambos Pissouros, senior analyst at IronFX Global.
"If new polls continue to show a tight race between the two campaigns as we approach the voting day, the outcome is likely to become even more uncertain and hence, volatility in sterling is likely to heighten further."
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