THE SNP's struggle to win over women voters in the referendum campaign is highlighted by a new poll for The Herald today.

The unique survey examining the attitude of voters to key players in the battle shows that First Minister Alex Salmond and his deputy Nicola Sturgeon both appeal to significantly more men than women.

However, the TNS BMRB survey also reveals major challenges for the No campaign, with low overall ratings for former Labour chancellor Alistair Darling, the head of the pro-UK Better Together campaign, and Prime Minister David Cameron.

Scotland Decides: read our new 20 page guide to next year's big vote

The Scottish Labour leader Johann Lamont emerges as a potential asset in appealing to women but 40% of voters do not know who she is, raising serious questions about her impact on the campaign.

The TNS BMRB survey asked more than 1000 voters to rate the five key figures on a scale of 1 to 10, where scores of 1 to 4 equated to "dislike", 5 to 6 was "neutral", and 7 to 10 was "like".

Mr Salmond and Ms Sturgeon had the highest average ratings, discounting don't-knows and those who have not heard of them, of 4.8.

They were followed by Alistair Darling and Ms Lamont on 4.3 and Mr Cameron on 3.6.

The First Minister and his deputy were both better liked by men than women, by 35% to 22% in the case of Mr Salmond and by 25% to 19% for Ms Sturgeon.

The findings reflected TNS's most recent poll on referendum voting intentions, which put support for independence at 30% among men and 22% among women.

The polling was conducted before the publication of the SNP's White Paper in independence, which included a headline-grabbing pledge to provide near-full-time free childcare by 2024 - a move seen as reaching out to women voters.

Writing in The Herald's latest Scotland Decides supplement, published today, Tom Costley, head of TNS Scotland, said: "Winning women's votes could be crucial for the SNP, as polls have long shown that women are less enthusiastic than men about the prospect of independence.

"Our survey of how people rate the key politicians in the referendum debate has found that women take a less favourable view than men of both Alex Salmond and Nicola Sturgeon."

He added: "In this referendum campaign, gaining approval among women could bring rich dividends."

Mr Salmond was the most liked of the five politicians (by 23%) and the second most disliked (by 40%).

Ms Lamont was the least liked (by 11%) and the least disliked (by 23%). Mr Cameron was the most disliked (by 57%).

An SNP spokesman said: "These are extremely positive figures for Yes - both among men and women, the First Minister and Deputy First Minister far out-poll all those in the No campaign. For example, around four times as many women and men like Alex Salmond compared to the dismal figures for Johann Lamont."

A Scottish Labour spokesman said: "Since Johann Lamont became party leader, we have led the way on the arguments against Scottish independence, and achieved big swings in two by-elections."