The survey for the Glasgow Herald newspaper showed 47 per cent of Scots likely to vote "yes" on the tax question in the 11 September referendum, 7 per cent less than a similar poll a month ago. Thirty-two per cent said that they would vote "no".
A clear majority are still in favour of the setting up of the parliament, however, with 61 per cent saying they would vote "yes" and 23 per cent saying "no".
Although the figures still show that a clear majority of those who have decided will vote "yes, yes", there was disappointment among campaigners for the parliament yesterday.
Recent polls, including some carried out privately for the Scotland Forward pro-devolution group, have shown a slow erosion of support for their cause.
The number of people undecided on the tax question rose in yesterday's poll from 19 per cent to 21 per cent, while those undecided on whether they wanted a parliament at all remained the same at 16 per cent.
There was further dissent over the referendum yesterday as Tam Dalyell, the long-time anti-devolutionist and MP for Linlithgow, called for the vote to be delayed. He told BBC Radio 4's World at One programme that because of the suspension of campaigning until after the funeral of Diana, Princess of Wales, on Saturday, people would not have had had enough time to make up their minds.
"This gives us precisely four days, three if you don't count Sunday, and for such a crucial decision there should be a longer campaigning time," he said.
The referendum could easily be postponed until May or June next year, he added.
Donald Dewar, the Secretary of State for Scotland, said on the same programme that the referendum would go ahead as planned, and he argued that the technical difficulty of recalling Parliament to stop it would be "formidable."
"I think people in Scotland are very well aware of the issues. We have had a very sad and tragic week but I think people will be able to move on from that ... they will be able to concentrate on what is undoubtedly an important vote and make their voices heard and their views known," he said.
Mr Dewar said that he had thought hard about the possibility of delay, but did not think the Scottish people were "so unsophisticated" that they could not grieve for the Princess as well as consider the issues involved in the devolution debate.
"I think people will want to get a decision taken. I think it is time for that decision after all these years of debate.
"I think that the feeling of uncertainty and anticlimax would in fact be regretted afterwards if we didn't push ahead," he said.
"I think it would be wrong, in fact, to call all this off and to start all over again at some uncertain, indeterminate future date. I think Scotland wants to make up its mind now."
The campaign had been longer than was normal in a general election, he added, and if the vote was put off it would have to be delayed for some time.
The national organiser of Scotland Forward, Paolo Vestri, said that the fall in support shown in yesterday's Glasgow Herald poll was disappointing. "However, there are many people who are still undecided," he said.Reuse content