While a vast majority of observers still expect May to emerge victorious on Thursday, a Survation poll published last weekend placed the prime minister’s ruling right-wing Conservative Party ahead by just a single percentage point.
In a hung parliament, with no party taking a clear majority, the U.K. could be thrown into a political deadlock with less than two weeks before formal Brexit talks were due to begin on June 19.
Macquarie noted that the U.K.’s “first past the post” system has meant elections were hard to call as the popular vote map doesn’t always match which seats were won and lost.
“There is a real risk that this general election could be used as a second referendum on the U.K.’s future relationship with the EU – a last gasp attempt to stop Brexit in its tracks,” Macquarie said.
“If a hung parliament does materialize, we think it could ultimately lead to a softer Brexit. But ironically, sterling is likely to fall initially.”
Macquarie noted that creating a new governing coalition would likely take weeks of “horse-trading” and “intense” uncertainty.
It also created the risk of a second referendum on Scottish independence, which would weigh sentiment, the analysts said.
In a 2014 referendum, Scotland voted to remain a member of the U.K., but the region also voted overwhelmingly in 2016 against Brexit, spurring rumblings of a fresh referendum.
Bank of America-Merrill Lynch was partially on-board with Macquarie’s view.
“With market nerves having increased in the final weeks of the campaign, we believe a large Conservative victory would be initially bullish for pound as it would remove the political uncertainty that has been building,” the bank said in a note on Wednesday.
The bank also didn’t expect that any pound rally would be long-lived, even if the Tories pull off a sweep.
“Large majorities are no guarantee that the pound will sustain its gains and with U.K. growth stalling, market complacency over the start of Brexit negotiations and positioning now broadly neutral, our bias would be to sell pound rallies,” the bank said.
If Labour manages to pull a rabbit out of a hat and take the majority, Bank of America-Merrill Lynch expected the pound would initially suffer a “steep” fall.
“Brexit will likely be the dominant driver of subsequent moves and here we think the initial sharp decline in the pound could be tempered if a Corbyn administration decides that its domestic policy agenda will take precedence over the Brexit agenda,” it said.
“Should it become clear that the Labour administration is moving toward a preference for single market access and therefore a softer Brexit, we think there is scope for a pound recovery.”
—CNBC’s Sam Meredith contributed to this article.