It’s not just Friday this week that will test sterling traders’ nerves. Thursday could also feel like feeding time at the zoo. On Friday, as the results of the UK’s referendum on EU membership roll in, is when the main action will happen. George Soros, no less, has warned that a Leave vote could lop 15 per cent off sterling, and who can argue with the great man? The options market certainly is not.

Would-be dip buyers are just itching to pounce. But timing is everything.

The global ripples are also a concern. A vote to leave would not be a black swan, given how long the vote has been coming, but if, as seems likely, it morphed into a global shock to markets, don’t be surprised to see the Japanese yen rocket into intervention territory. Disorderly market conditions would provide the perfect cover for the Bank of Japan to fight back against a rise. Brace, brace.

On the flip side, sterling’s storming rally last Friday and Monday when opinion polls showed more momentum shifting to Remain suggests that the currency is a coiled spring. If Brits vote to stay in the EU, a rapid rally into rates of $1.50 to the pound or more seems plausible.

But first: Thursday. The sensible thing to do is to nip to the polling station and then go for a long walk. In real life, though, news that some hedge funds have commissioned their own exit polls to try and get a lead on the result will mean that any flicker of action in the pound that day will be taken as a sign that someone, somewhere “knows something”. The usual polling day tumbleweed may not apply.

Resist the temptation to join in, says David Bloom at HSBC. Liquidity will be painfully thin. Any transaction, no matter how small, could have the capacity to hit the market disproportionately hard. Some speculative accounts could even try and fire up suspicions that Harry Hedge Fund has an early lead. And others may just take a punt.

“There may also be traders who have no conviction about the final result but simply believe that a skittish market is likely to panic at some point during the day. If they were to rationally sell in expectation of this, it might become a self-fulfilling prophecy,” says Mr Bloom. Good luck.

katie.martin@ft.com

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