Harry Potter film star Rupert Grint is challenging a ruling denying him a £1 million tax refund.
A tax tribunal previously rejected the actor’s appeal against an HM Revenue and Customs (HMRC) block on him using a change in accounting dates to shield his earnings from a higher tax rate.
The 30-year-old, who is calculated to have earned around £24 million from playing the character Ron Weasley in the Potter film franchise, has now taken his legal battle to the Upper Tribunal in London.
At a hearing on Wednesday, Mr Grint’s barrister Patrick Soares said the previous judge had applied the wrong legal test when deciding his case.
In an August 2016 ruling, Judge Barbara Mosedale described how Mr Grint had followed advice from tax advisers Clay & Associates to change his accounting date so that 20 months of income would fall to be taxed in 2009-2010.
The judge said Mr Grint wished to bring forward to the earlier year liability for payments on eight months’ worth of income otherwise due in the tax year 2010-2011 - the year the top rate of tax rose from 40% to 50%.
Her ruling added if the date change had been accepted it would have led to a 10% saving on income - about £1 million, according to Mr Grint’s accountants.
The judge stressed it was not part of HMRC’s case that Mr Grint - who admitted at the earlier hearing that his knowledge of his financial affairs was "quite limited" - was involved in tax avoidance.
She dismissed Mr Grint’s appeal, finding that he had failed to show a valid change in accounting dates because he did not have accounts showing the correct accounting period for the change.
But Mr Soares said: "In this case, the judge had really created a new test in determining what the accounts of the trader is for the purposes of income tax."
HMRC is contesting the appeal, arguing the judge made no error of law.
Mrs Justice Rose and Judge Jonathan Richards are expected to reserve their judgment.
Earlier this week, the actor told Radio Times magazine: "I actually don’t know how much I have. I couldn’t even really guess.
"It doesn’t really motivate me too much. It makes you comfortable, that’s the good thing about it, I think.
"I’m glad it’s there but I’m not really that focused on it."