Brian Chapman, 55, was on trial at the Old Bailey for double-claiming for hotels and international flights and pocketing refunds for cancelled flights between 2007 and 2011.
Chapman, who commuted from Scotland to London, had racked up £94,000 in credit card debts by 2011, the court heard.
But his wife Margaret said she was unconcerned about his gambling habit and was unaware of the full extent of his debts.
The part-time supply teacher and mother told the court she had never considered her husband to be dishonest, adding: "We have been married for 23 years. I know him very well."
Chapman, of Cumbernauld, North Lanarkshire, denied a single count of fraud.
A court official said the jury was discharged yesterday when it was unable to agree a verdict. The Crown will not be seeking a retrial.