Twice as many people believe Yes Scotland's campaign for independence has been the more effective in the run up to the referendum than its pro-UK rival Better Together, according to an opinion poll.

When asked which of the two lead organisations had run the more effective campaign, 45.5% said Yes Scotland had done a better job.

Less than a quarter (23.7%) said Better Together, which is led by former chancellor Alistair Darling, had been the more effective of the two campaigns, while almost a third (30.8%) did not know.

Polling company Progressive Scottish Opinion questioned 1,004 people about the effectiveness of the two campaigns ahead of the September 18 vote.

The research, which was carried out for public relations firm Orbit Communications, found almost half (48.9%) of undecided voters did not know which campaign had done a better job.

Of those who have still to make their minds up, 31.9% said Yes Scotland had been the more effective of the two campaigns, with 19.2% preferring Better Together.

Graeme Downie, director of Orbit Communications said: "Whilst it is obviously good news for the Yes campaign that voters see it as being the more effective campaign, they might be concerned that this has not yet translated into a lead on the referendum question itself.

"Perhaps it is more significant in predicting the outcome that Yes Scotland have a better perception than Better Together amongst undecideds. The main concern for Better Together must be that, if appreciation of the effectiveness of the Yes campaign continues to grow amongst undecideds, there is potential for the polls to narrow as we approach September 18."

He added: "Whilst the Yes campaign will be encouraged by these numbers, it will be a pyrrhic victory if they cannot convince voters to support them at the ballot box in September and Better Together would rightly be judged as having been the most effective campaign by achieving their desired result."

Yes Scotland's operations manager Sarah-Jane Walls said: "This poll is more confirmation of how the electorate positively regard the Yes campaign - and we believe that by winning the campaign, Yes will win the referendum. The Yes campaign is believed to be more effective than No by a factor of nearly two-to-one.

"Last month, a poll by Ipsos MORI had a similar finding, showing that 51% of voters saw Yes as running the best campaign, compared to just 23% for No.

"When one in five of No voters thinks the pro-Yes campaign is more effective, it highlights the difficulties for the No side - a campaign based on fear and scare stories.

"By contrast, we'll continue to take our positive message to every doorstep and community in Scotland - and we're confident that with less than 10 weeks to go, our vision for a fairer and wealthier Scotland will win the day."

A Better Together spokesman said: "All polls consistently show that the majority of people in Scotland are planning on saying 'no thanks' to separation in September.

"The last four polls have shown that people are making up their minds and they are deciding to vote no."