Scots campaigning for independence from the rest of the U.K. gathered support for a third straight month, while turnout at this year’s referendum is likely to be higher than in recent elections, according to the latest poll.

Backing for full autonomy for the Scottish government in Edinburgh rose two percentage points to 29 percent, while the proportion of voters wanting to keep the status quo advanced by a point to 42 percent, the TNS survey published yesterday found. People who said they were undecided declined to 29 percent.

Voters in Scotland will decide on Sept. 18 whether the country should leave the U.K. after 307 years and the debate recently has centered on plans to retain the pound should nationalists overturn the polls and win. Last week, Bank of England Governor Mark Carney made his first foray into the issue by meeting Scottish First Minister Alex Salmond in Edinburgh.

TNS said 65 percent of people are certain to vote, with 42 percent of the “undecideds” saying they will definitely cast a ballot one way or another. The 13 percentage-point gap in favor of staying in the U.K. widened to 17 points when using only respondents who said they were certain to vote, TNS said.

The pollster was commissioned this month by Scottish Independence Open Democracy and asked 1,054 eligible voters on Jan. 14-20. No margin of error was given. Respondents were asked the question that will appear on the ballot paper: “Should Scotland be an independent country?”

A Jan. 21-24 survey by ICM for the Scotland on Sunday newspaper found 37 percent of people would vote for independence, up five percentage points from a comparable poll in September. Those in favor of staying part of the U.K. dropped to 44 percent from 49 percent.