The pound slid to the weakest against the dollar since November after a poll by YouGov Plc showed the Scottish independence campaign gained a lead for the first time this year with the vote looming on Sept. 18. That extended last week’s biggest plunge in 14 months. A “Yes” vote would raise the prospect of a more cautious approach from the Bank of England, which this month kept its key interest rate at a record-low after persistent weakness in inflation and wage growth reinforced the case for maintaining emergency stimulus.

“This ensures that even if Scotland votes ‘‘No’’ next week the issue will not go away,” said Sam Tuck, a senior currency strategist at ANZ Bank New Zealand Ltd. in Auckland. “The GBP was under pressure as markets consider there to be little credible planning for a ‘‘Yes vote’’ with a large number of unresolved questions expected to cause a halt in business investment and keep the BoE on the sidelines should Scotland vote ‘‘Yes’’.”

The pound slid 0.7 percent to $1.6212 as of 8:31 a.m. in Tokyo, and touched $1.6165, the weakest since Nov. 26. It dropped 1.6 percent in the five days ended Friday, the largest weekly drop since July 2013. Sterling slid 0.7 percent to 0.7988 per euro. The dollar was unchanged at $1.2951 per euro and rose 0.1 percent to 105.18 yen.

Market Shocked

Following months of surveys that showed Scotland was unlikely to vote to leave the U.K., the latest results have shocked the currency market into action. One-month implied volatility, a measure of future price swings used to determine cost of options, surged 23 percent, the most since 2008, after the previous poll was released on Sept. 2.

“The referendum is on a knife edge,” Nick Stamenkovic, an Edinburgh-based fixed-income strategist at broker RIA Capital Markets Ltd, said yesterday. “Markets have been too complacent but are now waking up to the increased risk of Scotland voting for independence.”

The question of whether a go-it-alone Scotland will be able to keep the pound in partnership with the remaining parts of the U.K. has dominated the independence debate with all the major parties in London saying they would oppose it. Scottish First Minister Alex Salmond has argued they would change their view once negotiations began in the event of a vote favoring independence and has said Scotland would refuse to pay its share of the U.K. national debt if they didn’t give in.

RBS, Lloyds

A “Yes” vote for independence would prompt a significant increase in the volatility of U.K. assets, while the pound would fall against the euro and particularly the dollar, RIA’s Stamenkovic said in response to e-mailed questions.

Declines in the pound may also spark losses for “stocks with cross-border flows and trade,” including Royal Bank of Scotland Group Plc and Lloyds Banking Group Plc, according to Jeremy Stretch, the head of foreign-exchange strategy at Canadian Imperial Bank of Commerce in London.

“The risks are even higher” of a vote for independence after the latest polls, he said yesterday.

Uncertain Verdict

This weekend’s YouGov survey for the Sunday Times showed “Yes” voters increased to 51 percent, while the “No” side dropped to 49 percent, when undecided respondents were excluded. A separate poll, published by Panelbase, showed the independence campaign still needed to overcome a four-point deficit to triumph. Scotland votes on Sept. 18.

All three main U.K. parties said they would cede more control over policy making to the Scottish Parliament in Edinburgh after the latest opinion poll. Salmond dismissed the move as a “bribe” that wouldn’t sway voters.

Sentiment was already turning against the pound before the jump in support for Scotland’s independence. It’s tumbled more than 5 percent since touching $1.7192 on July 15, which was the strongest level since 2008. Sterling dropped 2.1 percent in the past month, the worst performer among 10 major currencies tracked by Bloomberg Correlation-Weighted Indexes.

Hedge funds and other large speculators are the least bullish on the pound since January, figures from the Washington- based Commodity Futures Trading Commission showed. The difference in the number of wagers on an advance against the dollar compared with those on a decline was 9,448 contracts last week, down from a net-long position of as much as 56,412 in July that was the biggest since 2007.

‘Severe’ Consequences

A win for Scottish nationalists may have “severe” consequences in the short term and spark a pound sell off, Goldman Sachs Group Inc. economist Kevin Daly said in a Bloomberg TV interview last week. BNP Paribas SA said a “Yes” vote would hurt U.K. government bonds as much as a credit-rating downgrade, while Standard Bank Plc’s head of Group-of-10 strategy Steve Barrow said it could push the pound down toward the mid-$1.50s.

“Given the importance of the vote on Sept. 18, the narrowness of the gap between the two camps and a market that, to date, has largely assumed that a ‘No’ vote was by far the most likely outcome, the danger is that the next few days sees a rush by investors to hedge their risks,” Simon Derrick, chief currency strategist at Bank of New York Mellon Corp. in London, wrote in an e-mailed note. “It therefore looks as if it could prove another dangerous September” for the pound, he said.