The pound risks a drop of as much as 10 percent in the event that Scotland votes to break away from the rest of the U.K., Morgan Stanley said.

“If the opinion polls were to become closer as the Sept. 18 referendum approaches, we would expect some risk premium to be reflected in U.K. asset markets,” Ian Stannard, head of European currency strategy in London, wrote in a client note dated yesterday. In that scenario sterling would “become vulnerable” as the political uncertainty prompts foreign investors to defer purchases, he wrote.

Polls consistently show a lead for the campaign to keep the union intact, though enough people are undecided to cause an upset. Support for Scotland breaking away was at 34 percent this month, compared with 45 percent for staying in the U.K., according to an ICM Research survey conducted for Scotland on Sunday. The proportion of voters who hadn’t decided which way to vote was 21 percent.

A victory for Scottish nationalists in the Sept. 18 referendum would probably push the pound down by between 7 percent and 10 percent on a trade-weighted basis, Stannard wrote in the report. Morgan Stanley, which owns the world’s largest brokerage, sees a 25 percent chance of Scotland opting for independence.

Sterling surged 11 percent in the past year against major peers tracked by Bloomberg Correlation-Weighted Currency Indexes as investors bet the Bank of England would be the first major central bank to end extraordinary stimulus measures. A Deutsche Bank AG gauge of the pound against major counterparts including the dollar, euro and yen was at 84.56 at 1:42 p.m. London time, after climbing to 84.71 on July 7, the strongest level since November 2008.

The pound rose 0.4 percent to $1.7159 today after a report showed consumer prices rose in June at a faster pace than economists had predicted.