He told a court they were taking action as a “point of principle”.
Dr Neil Murray said Amanda Donaldson was employed to organise his wife’s business and professional matters.
She was suspended and later dismissed in 2017 over alleged unauthorised spending that included £3,629 in retailer Molton Brown, £2,139 in card shop Paper Tiger and more than £1,800 in Starbucks and Costa coffee shops. Rowling claims Ms Donaldson wrongly benefited from the credit card and by taking Harry Potter merchandise to a total value of almost £24,000 and is seeking damages in the civil case.
Ms Donaldson denies the claims. Asked by the author’s lawyer why one of the country’s wealthiest people is pursuing an action over a relatively small amount of money, Dr Murray, 47, said: “I would say there is a matter of principle here. I firmly believe Amanda has stolen a substantial amount of money and Harry Potter merchandise that was for sick and dying children.
“She continues to deny any of it. I feel personally that we have a duty to protect any future employer. If this was a small business she could have ruined it.”
Airdrie Sheriff Court heard Dr Murray was a co-manager of his wife’s business affairs and an accountant raised concerns with him over the personal assistant’s spending between 2014 and 2017.
He said the biggest concern was over cash withdrawals of £400 and £250 in December 2016 that Ms Donaldson claimed were for a Christmas lunch deposit at Castle Terrace restaurant in Edinburgh.
Chartered accountant Steven Simou earlier told the court he had contacted the restaurant and found no deposit had been requested or taken off the final bill.
In his evidence, Dr Murray, said an email Ms Donaldson claimed to have received from the restaurant confirming the deposit was in fact faked by the former PA.
He said: “The restaurant confirmed no deposit was taken and no email was sent. I believe she fraudulently created that email in order to justify that spend.”
Dr Murray told the court he challenged Ms Donaldson over the money in “an astonishing encounter”.
He said: “She shut down, was calm and basically lied. At the end of the encounter I was really taken at how good a liar she was.”
Ms Donaldson’s lawyer said Dr Murray was carrying out a “character assassination” of her client.