Savanta ConRes research, carried out for the Scotland on Sunday newspaper, found that 46 per cent of the 1,015 Scots polled were in favour of remaining part of the United Kingdom, while 43 per cent supported independence and 10 per cent were undecided.
With undecided voters excluded, 52 per cent to 48 per cent of Scots indicated that they were in favour of the union.
This marks a shift from a Savanta ConRes poll conducted in late February, in which a majority of Scots indicated they backed independence and 71 per cent said the country would “fare better” outside the UK.
The row over the Scottish government’s unlawful investigation into Alex Salmond, the former first minister, appears to be damaging the SNP’s image.
The poll, taken two days after Ms Sturgeon appeared in front of a Hollyrood inquiry into the matter, found that more than a third of Scots would be less likely to vote for independence because of it.
Some 43 per cent said that their trust in Ms Sturgeon has fallen as a result of the inquiry, in which the SNP leader defended herself against accusations that she misled parliament about her knowledge of allegations against Mr Salmond.
Ms Sturgeon added that the suggestion she plotted against her former ally was “absurd” and “not based in any fact”.
But while trust in the first minister may have fallen, trust in Mr Salmond has plummeted, with 57 per cent of people polled saying they believed Mr Salmond, who also appeared at the inquiry, less than they did before.
Mr Salmond accused Ms Sturgeon of conspiring to politically sideline him and of breaking the ministerial code by lying about when she learnt about assault allegations against him, which she strongly denies.
Mr Salmond has previously been awarded £512,250 after it was ruled than an investigation into his conduct was carried out unlawfully.
Responding to the survey, a spokeswoman for the SNP said: “With Scotland on Sunday and Savanta Comres themselves stating that this poll is not comparable to previous polls and has not been properly weighted, it should be treated with caution.”
Savanta ComRes associate director Chris Hopkins said: “With only a fifth of 2014 ‘No’ voters less likely to support independence because of the saga, its impact on the first minister doesn’t look to be catastrophic – for now.”
The SNP will face Scottish parliament elections in May.
