He was challenged after claiming “Tory cuts” had left the Scottish Government with less money over the years.
However, shadow finance secretary Murdo Fraser pointed out his own budget document shows the funding from Westminster has actually increased from when the Conservatives came to office in 2010.
Mr Mackay was unable to explain the contradiction, prompting Mr Fraser to describe him as the luckiest finance secretary in Holyrood’s history, given he has the most money to use.
Later in the meeting, Mr Mackay also confirmed it was his intention to use new borrowing powers “to the max”, meaning £450 million will be borrowed next year.
Scottish Conservative shadow finance secretary Murdo Fraser said:
“It is astonishing that the SNP finance secretary appeared not to have read his own documents, which clearly contradict the nationalist mantra of ‘Tory cuts’.
“Total spending is up in real terms over the period of office for this and the previous Conservative government.
“Derek Mackay did confirm that the Scottish Government’s budget has risen in real terms by £501 million against the current year, meaning that he has half-a-billion more to spend next year.
“He’s the luckiest finance secretary in the history of devolution – his budget is higher than that of any of his predecessors.
“It’s just a pity he doesn’t want to admit it.
“The SNP now needs to drop its inaccurate claims about ‘Tory cuts’, which its own budget disproves.
“And perhaps if Mr Mackay spent more time on the day job, instead of promoting a disastrous and unwanted second independence referendum, he might have the chance to read and understand his own budget.”
On the SNP’s borrowing plans, Mr Fraser added:
“Now that the Scottish Government has significant borrowing powers, it’s right that it uses them to boost the economy and public services where possible.
“But at the same time, this will be a test of the SNP’s financial competency.
“Too often in the past we have seen huge cost overruns, and millions wasted, on public sector projects.
“Now that the SNP has a credit card to use it needs to spend this extra money more carefully than it has in the past.”