Labour's increasing irritation with poor opinion poll findings boiled over yesterday when Paul McKinney, the Scottish party's new campaign director, savaged a television survey which suggested Scots found Alex Salmond of the SNP a potentially better Scottish First Minister than Donald Dewar.

After months of increasingly depressing findings for Labour across a range of opinion polls, the Scottish 500 survey for Scottish Television's Platform programme provoked Mr McKinney, a former STV employee, to denounce it as ''polluted'' and ''extremely dubious''.

His attack marked a further worsening of relations between Labour and the television station after a recent behind-the-scenes row when Labour complained about the treatment of Jim Murphy, MP for Eastwood, during a debate on the party's New Deal for young unemployed. STV declined a Labour request for a section of the recorded programme to be edited.

While the SNP exulted in yet another poll publicity coup yesterday Mr McKinney derided Scottish 500's reliability after it gave Mr Salmond a 47% approval rating as possible Scottish First Minister compared with Mr Dewar's 37%.

''This was not a poll and it is now no more than a very suspect sample . . . it breaks every rule in the polling book. It is not representative and it should be discounted,'' Mr McKinney insisted.

He was supported by Anne McGuire, Labour MP for Stirling and parliamentary private secretary to Mr Dewar, the Scottish Secretary. She described Mr Dewar as a tremendously popular figure and a man of great integrity. ''He has delivered and is continuing to deliver for Scotland. This Government is delivering on the issues that matter most to Scots - better schools, a better health service and a New Deal on jobs.''

When STV's same sample was asked if it thought Scotland would become independent, 67% responded that there would be independence within 20 years, and 79% predicted it would happen within 50 years.

The STV poll is based on the views of 500 people who were first asked their party preferences on the eve of the General Election. Their opinions have been tracked in several polls since then. Last week they suggested the SNP was comfortably leading Labour in voting intentions for the Scottish Parliament.

Mr McKinney, who worked for Scottish TV as a news programme producer until he was recruited earlier this month by Labour, recalled that the 500's General Election prediction had put the SNP 10 points ahead of their result on May 1. This showed the survey was flawed right from the start, he said.

''And now the 500 has been whittled down to about 320 - it is not 500 at all.

''This poll has become extremely polluted. People are dropping out all the time, the findings are obviously distorted to the point that this poll simply cannot be relied on at all. It is an extremely dubious survey.

''We had a discussion with Scottish Television about all this and we explained our doubts. In response they said they would make clear how the figures were being arrived at but they completely failed to do so. They are being very disingenuous about the whole thing.''

But SNP chief executive Michael Russell said the poll was excellent and proved the Nationalists were leading the Scottish political debate. ''The survey showed that Alex Salmond is the most popular choice to be Scotland's Prime Minister - just as it showed the SNP ahead of Labour for the Scottish Parliament election. The SNP can build on these solid ratings in the months ahead and emerge as the first party in the Scottish Parliament with an SNP First Minister.''

An STV spokesman said: ''We don't accept for a moment we are being disingenuous. There seems to be no dispute about the sample being 320 - fieldwork was carried out over Easter when many people were away on holiday.

''We don't have any information to support the suggestion that this poll is dubious in any way.''