THE decision by the main UK parties to reject Alex Salmond's plan for a currency union between an independent Scotland and the rest of the UK has made undecided Scots more likely to vote No, according to the latest poll.

It found 34% of undecided voters said they were more likely to vote No as a result of the move, against 16% who felt they were more likely to vote Yes. The biggest proportion - 44% - said ruling out a pound-sharing sterling zone had no impact on their views.

The poll comes three weeks after Chancellor George Osborne, backed by his Labour and Liberal Democrat opposite numbers, warned the UK would not enter a monetary union with an independent Scotland.

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The headline figures showed that of those certain to vote, 32% backed Yes, 57% No and 11% were undecided.

Support for Yes was down two percentage points on a similar survey in December, while backing for No remained unchanged.

Stripping out the don't knows - seen by some polling experts as the most reliable indicator of the public mood - the No campaign leads 64% to 36%.

The Ipsos Mori poll for STV News also showed a continuing gap between men and women.

It came as Deputy First Minister Nicola Sturgeon used a speech in Glasgow to step up efforts to win over female voters.

The survey questioned 1001 over-16s between February 20 and 25. It found support for independence among men was 38% and 27% among women. It also showed much higher support for independence in less well-off areas.

Backing for a Yes vote outstripped No at 47% to 41% in the most deprived areas. The position was reversed in the most affluent areas, where No was on 71% and Yes on 20% on average.

Mark Diffley, director at Ipsos Mori Scotland, said: "The important recent debate over currency appears not to have shifted committed voters from their positions, while undecided voters appear a little more inclined to vote No as a result. Having said that, overall support for a No vote has not changed since December."

Speaking in Glasgow, Ms Sturgeon agreed the Yes campaign had to do more to win over women voters. Answering questions at a Scottish Council For Development And Industry event, she said: "If we win over a majority of women we will win the referendum. It is one of the big challenges those of us on the Yes side face over the next few months."

Attacking the pro-UK parties' emerging plans for further devolution, she said they did not pass her "childcare test," a reference to the SNP's proposal for universal childcare by 2024 which, the party claims, could be achieved only under independence.

Ms Sturgeon also made an emotional appeal, claiming No voters as well as Yes supporters would "feel a sense of regret" if the chance of independence was rejected.

Repeating her offer to include pro-UK figures in the talks that would follow a Yes vote, she made an "open offer" to Alistair Darling to join the negotiating team. Mr Darling, the head of the pro-UK Better Together campaign, dismissed the offer but welcomed the poll results.

He said: "This poll makes clear that Alex Salmond's failure to tell us what would replace the pound if we left the UK is costing the Nationalists support. The idea that voters can be expected to go to the polls blind on the most fundamental issue affecting our economy is simply not credible."

Blair Jenkins, chief executive of the pro-independence Yes Scotland campaign, said: "The No campaign - Project Fear - has played what it clearly believed was its ace card when George Osborne said he would not share the pound with an independent Scotland. But it has not had the impact the No campaign would have been hoping for."