The sluggish economy is the chief worry among millionaires, while those with over $5 million in investable assets fret about the national debt, according to a new report from Spectrem Group.

Worries over the economy have actually increased since this time last year among millionaires, prompting investors to make changes to their portfolios, according to the report.

Four out of five millionaires now cite “the sluggish economy” as their chief concern, compared to 70 per cent a year earlier. The proportion of mass affluent investors who viewed this as the key concern also rose over the same period, from 74 per cent to 81 per cent.

However, among survey respondents with at least $5 million investable assets, the top worry was not slow economic growth in itself but the national debt, cited by 82 per cent, and the “contentious political environment,” cited by 80 per cent. The economy came in third place.

Such worries over the political environment and the national debt may be due to fears they will spark a much more difficult climate for the very wealthy - particularly as regards taxation - as this segment of society has received much attention lately from, for example, the Occupy Wall Street movement.

In the latest Wealth Report from Citi and Knight Frank, Tina Fordham, senior global political analyst at Citi, said that the dissatisfaction over income inequality manifested in the OWS movement would likely continue and could lead to “a long-term recalibration between governments, businesses and society as a result.”

“Governments may use more taxation instruments and globally there may be a further attack on tax havens. Recent governmental and intergovernmental activity in these areas is not a passing phase,” Willem Buiter, Citi’s chief economist said in the report. “It’s going to be a tougher playing field for the rich.”

Indeed, 70 per cent of UHNW investors in the Spectrem survey (defined as $5 million+ investable assets) are anxious about changes to the tax code, as are 65 per cent of millionaire investors and 64 per cent of mass affluent investors.

So far, fears over tax rises have caused 40 per cent of UHNW investors to adjust their portfolios, 28 per cent of millionaires to do so, and 25 per cent of mass affluent individuals.

Meanwhile, investors from all three categories of wealth appear roughly split on whether their financial positions will improve this year, with around half saying they will.