Scottish Conservative leader Ruth Davidson has been accused of committing a Mitt Romney- style gaffe ahead of her appearance at the Tory Party annual conference.

The SNP seized on extracts released ahead of her speech today in which she said just one in eight Scots, 12%, was a "net contributor".

She called Scotland a "gangmaster" state due to the high proportion of the population who work for the public sector.

The SNP accused her of a gaffe on the scale of US presidential candidate Mr Romney.

He was secretly taped telling donors he did not concern himself with 47% of voters whom he said paid no income tax.

The Conservatives said they stood by the figures – which they said came from the 2010/11 Government Expenditure and Revenue Scotland report.

But SNP MSP Kenneth Gibson called on Miss Davidson to apologise.

He said the comments were her "Mitt Romney moment", adding: "At least Mitt Romney only insulted around half of Americans though, while Ruth Davidson believes almost 90% of Scots do not contribute to society.

"It is an outrageous slur, and [she] should apologise to the people of Scotland."

Miss Davidson is expected to tell a fringe event at the conference, in Birmingham: "It is staggering that public sector expenditure makes up a full 50% of Scotland's GDP and only 12% of people are net contributors, where the taxes they pay outweigh the benefits they receive through public spending."

She is also due to add: "Only 12% are responsible for generating Scotland's wealth. I wonder how many of them work on public-sector contracts?"

The extract went on: "If the gangmaster state is the only provider people can see for their housing, education and employment, it's no surprise those who seek to break the stranglehold find barriers in their way."

Her team later made clear Miss Davidson would refer to 12% of households.

A Tory source said the Scottish Conservative leader was not giving a message to voters, but was pointing out "economic reality".

She will also accuse Labour and the SNP of still blaming the Conservative Party "for the problems they have created – and are continuing to create".