Holidaymakers heading abroad this summer have been flocking to snap up their travel money ahead of the EU vote.
Post Office Travel Money, which accounts for one in four of all UK foreign exchange transactions, said currency sales overall have surged by 74% year-on-year since the weekend.
It said on Tuesday that Post Office branch sales were up by 48.8% on the same period a year ago, while online purchases were up by 381%.
The value of the pound has see-sawed amid the uncertainty over whether the UK will decide to remain in the EU or vote for a Brexit.
The pound has made some gains in recent days, rebounding from two-month lows against the dollar and the euro a week ago when Brexit concerns sent it plunging. There have been warnings that a Brexit vote could trigger further falls in the pound - and some holidaymakers may be hedging their bets by changing their money ahead of the vote.
The Post Office saw a spike in currency sales over the late May Bank Holiday weekend and it said the pattern of growth has continued since then.
Post Office Travel Money said in a statement: "Currency sales remain buoyant and are up 36% year-on-year for June to date in Post Office branches, online and through purchases on its pre-paid travel money card. This rises to a dramatic growth of 154% for currency purchases made online - the majority of this for euros and US dollars."
Despite the surge in demand, the Post Office said it is stocked up and has ready availability of euros for purchase in its branches and online.
Meanwhile, international money transfer specialist HiFX reported the number of holidaymakers buying euros and US dollars has increased by 46% since the weekend.
Chris Towner, chief economist at HiFX, said a prepaid currency card, which people can load with cash now to use abroad, could be a possible option for people wanting to lock into an exchange rate now.
He said: "As the big day approaches, the polls are still neck and neck, the pound is experiencing intense fluctuations."