High earners could move away from Scotland to escape an income tax gap with the rest of the UK, a leading economic think tank has said.

David Phillips, head of devolved and local government finance at the Institute for Fiscal Studies, said the wealthy could also take other measures to avoid paying more.

It comes after UK Chancellor Kwasi Kwarteng announced the scrapping of the top rate of income tax for those earning £150,000 a year or more, as well as a cut in the basic rate to 19p in the pound.

The measures do not apply in Scotland, where control over income tax rates and bands is devolved.

If the Scottish Government does not follow suit, everyone earning more than £14,732 will pay more income tax in Scotland compared to the rest of the UK.

Someone on £30,000 would pay £195.80 more next year, while those on £50,000 would pay £1,863.40 more.

High earners in Scotland would pay an additional rate of 46 per cent on earnings of more than £150,000, while those in the rest of the UK would pay 40 per cent.

This means someone earning £200,000 in Scotland would pay £6,045.80 more, according to the Chartered Institute of Taxation.

First Minister Nicola Sturgeon has already strongly indicated she will not replicate the tax cut for high earners.

Mr Phillips told The Scotsman: “There is limited evidence so far on the responsiveness of the highest earning Scots to differences in tax rates between Scotland and rUK [the rest of the UK] – so far the difference in marginal tax rate is just 1 per cent (although the difference in average is somewhat higher because of the lower higher rate threshold too). So we haven't got any quantitative prediction of what would happen.

"However, I would expect a difference of 6 percentage points in the top marginal rate to have a more significant impact on taxpayer behaviour. One response could be to move from Scotland (or similarly not move to Scotland).

"Those high income Scots with a home in both Scotland and England (e.g. that work partly in London) could rejig their time so they spend a bit more time in England and so can pay the lower UK Government tax rates.

"It’s also worth noting that people don't actually need to move – they could incorporate and so take their income in the form of dividends, on which UK rates will continue to apply.

"This is likely to become easier again following plans to repeal the IR35 rules which made employers assess whether someone should actually be taxed as if they were an employee.

"I wouldn't want to predict what the SNP will actually do – although it is worth noting that they raised the risk of substantial behavioural response from a bigger gap in tax rates as a reason not to increase the Scottish additional rate to 50 per cent as argued for by Scottish Labour.”

One of Scotland's leading lawyers previously said he would have to "consider" moving to England if the widening income tax gap is not addressed.

Roddy Dunlop KC, Dean of the Faculty of Advocates, tweeted: "I’ve lived in Scotland all my days. I love this place. I do not want to leave. But if there is this level of tax difference, I’d have to consider it. Northumberland is nice, apparently."

He described a tax gap of 6 per cent as "madness" and said it would put off higher earners from moving to Scotland.

He said: "Why would they, when even those properly devoted to the country are considering their options?"

After his comments sparked a row on Twitter, Mr Dunlop clarified: "Look: I’m going nowhere: I’d just like to pay the same tax as everyone else. If that makes me greedy, fair enough."

High earners could move away from Scotland to escape income tax gap, says IFS