By Josie Cox and Tommy Stubbington 

The British pound plummeted to a near nine-month low against the U.S. dollar Monday, while Scotland-focused stocks also fell, whacked by a poll over the weekend showing that the number of those favoring Scottish independence had eclipsed those opposing a split for the first time since the referendum campaign began.

Sterling dropped more than 1.3% to $1.6105, marking its lowest level since November last year, while the euro gained 0.8% against the pound to GBP0.8037. Citigroup said in a note that sterling could now easily slump to $1.56 in the event of a 'yes' vote, while some investors predicted it could fall even further.

Paul Lambert, head of currency at Insight Investment, which oversees $472 billion of assets, described the shift in polls over the last weeks as "dramatic."

"The vote has moved from being something three or four weeks ago that we didn't need to focus on, to something we need to think about [in terms of] how it affects our portfolios," he said.

"Investors are having to address a lot of questions about the implications of independence that they would prefer to avoid because they are complicated and difficult," he added.

In equity markets Monday, companies that are considered to have most exposure to the Scottish economy, through their customer bases or revenue generation, were most impacted.

Royal Bank of Scotland Group PLC shares fell 2.9%, making the lender one of the biggest losers on London's FTSE 100 index, followed closely by Scottish-domiciled names such as Standard Life PLC and SSE PLC.

BNP Paribas credit strategists Gildas Surry and Geoffroy de Pellegars wrote in a note that a vote for independence could "significantly impact " RBS's credit rating as well as increase compliance, operational and funding costs. The FTSE index was 1% lower early afternoon, having last week hit a 14-year intraday high.

The latest YouGov poll released Saturday showed 47% of those surveyed were now likely to vote "yes" to independence, while 45% would likely say "no." The rest of the 1,084 voters polled Sept. 2-5 said they were undecided or wouldn't vote.

Paul Donovan, an economist at UBS, said that even if the pro-unionists took the lead on September 18, the latest figures raise the risk of what he dubs a "Québécois scenario"--a narrow rejection of independence that leaves open a risk of a further vote. "We believe this would have implications for banking, gilts, direct investment into Scotland--from overseas and the rest of the United Kingdom--and sterling, " he said.

Alastair Thomas, head of rates and treasury at ECM Asset Management, meanwhile, stressed that whatever the outcome the impact was likely to be prolonged. In the event of a "yes" vote, he said, it could take up to 18 months before all the details are agreed.

"One could even imagine a delay in the start of U.K. rate hikes due to economic uncertainty, which is why sterling is being sold this morning," he said.

Already last week, the currency came under severe pressure as polls showed a narrowing of the two camps. Gilts and equities underperformed moderately too, while implied volatility rose.

On Monday, currency strategists at Barclays said that derivatives that protect users from sharp shifts in sterling are seeing ferocious demand.

"The abruptness of the shift in one survey should be viewed with caution, but nonetheless reinforces our long-held view that Scotland's independence referendum is a serious event risk, not a tail risk," they wrote.

The currency has now fallen more than 5% from its high in July of $1.7190.

In government bond markets Monday, the moves were more muted,

The yield on the U.K.'s 10-year gilt contract was at 2.490%, around 0.02% higher on the day and broadly in line with a move in German government bonds. Yields rise as bond prices fall.

Nick Gartside, chief investment officer for fixed income at J.P. Morgan Asset Management, which manages $1.65 trillion of assets, said that this was chiefly because the debate isn't materially impacting the U.K.'s perceived ability to service its debt.

"In the U.K., that is exceedingly high and will be no different following any vote or poll," he said.

Back in equities, there are also some investors who are suggesting a silver lining for markets.

"In general, the U.K. consumer sector was hit quite hard by sterling strength," said Colin McLean, managing director and founder of Edinburgh-based fund manager SVM Asset Management. "I think generally a weaker pound could support, especially some of the retailers, as well as other consumer sector names," he added.

"Nobody likes uncertainty and we aren't belittling its ramifications, but there are definitely possible positives," said Philip Lawlor, partner at London-based asset manager Smith & Williamson Investment Management LLP, with approximately GBP15 billion under management.

Rebecca Howard and Anjani Trivedi contributed to this article.

Write to Josie Cox at josie.cox@wsj.com and Tommy Stubbington at tommy.stubbington@wsj.com

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