Alex Salmond's personal popularity was not thought to be a key factor

Researchers led by Strathclyde University found little evidence that the Iraq war or Labour's record at Westminster was to blame.

The SNP won in the May election because voters saw them as a more positive alternative, the report said.

It said it was largely a "Scottish election" in which devolved matters were uppermost in voter's minds.

The SNP returned 47 MSPs after the Scottish Parliament election, one more than Labour, and went on to form a minority government.

The Scottish Election Study 2007 surveyed more than 1,500 voters before and after polling day.

Personal popularity

The SNP win had been heavily put down to Westminster-related problems for Labour such as the Iraq war and the cash-for-honours controversy.

The team of academics from Strathclyde, Sheffield and Lancaster universities found that voters were more positive about the SNP's likely performance than Labour's record.

They also found there was no evidence that Mr Salmond's lead over Jack McConnell in terms of personal popularity was a significant factor in the Nationalists' win.

Dr Robert Johns, lecturer in politics at the University of Strathclyde, said: "The key issues, particularly the economy, seem to be those that are more about how the parties will perform, rather than the specific policies and standpoints that they adopt.

"On balance, voters were rather negative about Labour's performance and fairly optimistic about that of the SNP.

It does seem that a key element of the SNP's success was projecting a positive image Dr Robert Johns University of Strathclyde

"Indeed, it does seem that a key element of the SNP's success was projecting a positive image."

The study found that the voting did not follow class lines.

Support for independence fell compared with 2003, but the Nationalists were able to attract a third of those who backed more powers for the Scottish Parliament.

Dr Johns said: "It (the SNP) persuaded people that it can govern under devolution, while retaining very strong support from advocates of independence."

The SNP was found to have stronger support among male voters and voters aged over 60 but trailed Labour by 13% among constituency voters aged under 30.

The Nationalists also had a lead over Labour on devolved matters including education, health, crime and transport.