By Belinda Goldsmith
LONDON (Reuters) - With a year until Scotland's referendum on independence, enough voters are "don't knows" to swing the vote and only one in four are certain to vote for separating from Britain, according to an opinion poll on Wednesday.
The survey follows a flurry of warnings from British government figures this year on the potential negative economic impact of independence. Finance minister George Osborne said this week it would make Scotland four percent poorer over the next 30 years and over-dependent on volatile tax receipts from the oil and gas industry.
Scottish nationalists dispute that claim and argue a fully independent Scottish parliament could attract investment through lower taxes and could utilize oil revenues more efficiently.
Wednesday's survey showed that 28 percent of respondents were uncertain about quitting the 300-year-old union, up 13 points from six months ago. The "yes" camp fell to 25 percent from 33 percent, the lowest level of support since polling on independence started in 2007.
Support for an outright "no" was also down, at 47 from 52 percent, the TNS BMRB poll showed.
"The high number of don't knows could turn out to be the most significant factor in how the referendum campaign develops," Tom Costley from TNS Scotland said.
"Both the Yes and No camps have lost ground in 2013, which suggests that neither campaign has yet succeeded in making a strong connection with the voters in Scotland."
Lobby group Yes Scotland also said the most significant figure in the latest survey of 1,017 Scots, conducted between August 21 and August 27, was the rising number of uncertain voters.
Among 16 to 34 year olds, 29 percent said they would vote for independence but only 45 percent were certain to vote, while 70 percent of the over-55s said they would vote but only 20 percent would support a split.
Younger voters were more inclined to support independence but also the least likely to vote, the poll found.
A YouGov survey this week showed 59 percent would vote against independence, an increase of four points on a similar poll 10 months ago, while one in 10 people were undecided.
The latest surveys were released as it was reported that Scottish First Minister Alex Salmond's main adviser, Kevin Pringle, was moving to Yes Scotland.
The move was widely seen as an attempt by Salmond to shore up the SNP's (Scottish National Party) influence in the Yes campaign and bolster backing for independence in opinion polls.
The SNP holds 65 of 129 seats in the Scottish Parliament.
(Editing by Louise Ireland)