SCOTLAND'S top 1% of earners have seen their salaries increase at a faster rate than other workers over the past decade, according to a new report.

The country's 25,000 highest earners saw their share of total pre-tax incomes soar from 6.3% to 9.4% between 1997 and 2009, the Economic and Social Research Council (ESRC) study showed.

Meanwhile those in the bottom 5%-10% of earners fell further behind average wages.

The trends have driven growing income inequality in Scotland. Workers in the top 1% now earn 20 times as much as those in the bottom 1% on average.

The report said the increase in salaries at the top end was linked to the "growth in the financial sector, bonus pay and a globalising market for 'superstar' CEOs and financial managers".

Increased part-time working was among the reasons for the lowest paid slipping further behind average wages, economists David Bell and David Eiser found.

Meanwhile, the share of higher-paying and lower-paying jobs increased between 2001 and 2010, while the share of middle-wage jobs fell as a result of "technological change and globalisation," their report said.

The ESRC backed the study to inform the independence debate. The pro-independence Yes Scotland campaign has made the UK's high levels of inequality a key part of its case.

Professor Bell said: "Though an independent Scotland would have more powers to address inequality, its room for manoeuvre would be constrained by these wider forces.

"Inequality in Scotland, like in many developed nations, is partly being driven by technology, by trade, and even by how we decide to form households.

"So there are likely to be limits to the extent that a small open economy can reduce inequality. Scottish independence would provide opportunities, but the constraints that already exist would not go away."

The study found levels of inequality in Scotland were lower than in the rest of the UK, mainly because of the huge gulf in earnings in London.

In the UK capital the top 1% of earners took a 14% share of total pre-tax income in 2009, up from 8% in 1997.

However, despite growing ­earnings inequality, relative net household incomes have remained steady since the mid-1990s, as taxes and benefits have helped redistribute wealth.

Compared with other developed countries, however, especially Nordic nations, inequality remained high in Scotland and the UK as a whole.

Those earning over £86,000 in 2010/11 were in the top 1% of the adult population in terms of income. Those earning over £70,000 were in the top 2%.

The top 1% of income taxpayers were those earning over £108,000 from their jobs. The top 2% of income taxpayers earned over £79,000.

The report said an independent Scotland would be able to target the very top earners with higher income tax, but warned they may find ways to avoid paying it.

It said: "The rise in the share of top-income earners in total income arguably provides scope for an independent Scotland to adopt a more progressive form of income taxation.

"In considering reform to tax policy, an independent Scotland would need to bear in mind the relatively high propensity of top-earners to shift their income from one jurisdiction to another, or to record it in other ways."

It added that there was "some evidence that the Scottish electorate would be more supportive" of reforms to employment tax and benefits policy compared to voters in other parts of the UK.