Labour has edged ahead of the SNP in voting intentions for the Scottish Parliament, according to a poll published last night.

But the same poll shows contrasting figures for the leadership ratings, with the SNP's Alex Salmond placed far ahead of his rivals in other parties.

The confusing conclusions have caused a leading polling expert, Professor John Curtice of Strathclyde University, to cast doubt on their reliability.

The First Minister was reckoned to be doing the best job by 65% of those questioned, while Wendy Alexander, the Scottish Labour leader, was seen as the best performing leader by only 17%.

Annabel Goldie, the Scottish Conservatives chief, was on 11%, and Nicol Stephen, the LibDems leader, was on only 6%.

On Holyrood voting intentions for both the constituency and regional votes, the Nationalist government has slipped behind its main opponent, according to the Progressive Scottish Opinion polling company.

The survey of 1034 adults, questioned from January 3 to 8 for STV's Politics Now programme, found that Labour had a one-point lead over the SNP on the constituency vote, by 37% to 36%. Conservatives were on 13% and LibDems on 12%.

At last May's elections, on the constituency vote, the SNP won nearly 33%, Labour won just over 32%, Conservatives had 17% and LibDems 16%.

On the regional vote, by which 56 list MSPs are elected, Labour had a wider margin over the SNP, by 38 to 34%. Conservatives were on 14% and LibDems on 11%, while Scottish Greens registered 2% backing and 2% for others.

On the list vote last May, the SNP had 31% to Labour's 29%, while Tories had 1% and LibDems 11%, with Greens winning only 4%.

Professor Curtice said of the poll: "I would exercise extreme caution before I would take this as any evidence that the Labour Party has staged any kind of significant recovery in Scotland."