LORD Ashcroft, the Tory donor, has been accused by the SNP of committing a gaffe by conducting a poll that showed 50% of Scots did not want Trident retained in an independent Scotland while only 35% did.

The Nationalists said the Tory faced embarrassment because the poll was conducted to show "more than half of Scots are in favour of nuclear weapons" when they said the survey showed only 37% believed this in principle compared to 48% who did not.

"It in fact confirms Scottish opposition to nuclear weapons being based here," said Angus Robertson, the SNP defence spokesman. "Just 37% of Scots support the UK having nuclear weapons and even less, 35%, would want Trident to stay in Scotland after independence."

"Only a Yes vote next September can get rid of Trident for Scotland so that we can spend Scotland's share of this money helping to build a fairer society and stronger economy," he said.

When asked, in principle, where they stood on the UK retaining nuclear weapons, 37% of those polled said they were in support, 48% were opposed and 15% said they did not know.

Asked what should be done when Trident comes to the end of its life, 20% supported a like-for-like replacement, 31% a cheaper version, 34% scrapping it completely and 16% did not know.

When the £20 billion to £25bn replacement cost was included in the question, the respective figures were 24%, 29%, 36% and 11%.

Asked if Trident should continue to be based in Scotland, 43% said yes, 39% no and 18% did not know.

Asked if the UK's nuclear deterrent should be based in Scotland in the event of independence, 35% said yes, 50% said no and 15% did not know.