Williams had filed PAYE tax returns in relation to up to four employees for the bar, which was also known as On Tap, but an IRD investigation later uncovered that up to 10 had been working there.
The couple, who are also well known in horse-racing circles, were responsible for the management and operation of the restaurant and bar. Williams oversaw banking, employment and tax affairs. Stewart worked in the restaurant and kitchen but had access to the company bank account.
On October 22, 2013, Inland Revenue executed search warrants at the restaurant and at the couple's home, where investigators discovered a diary containing details of the pub's daily sales between January 1 and October 21, 2013.
An analysis of the diary discovered an additional $157,706,11 worth of sales that were not declared in GST returns.
Data recovered from the cash register showed the company received, on average, 29 per cent of its sales in cash. However, only 3 per cent of cash takings were deposited into its bank account.
The couple also received cash payments that were not recorded through the till.
Williams told IRD investigators that the company's PAYE tax returns were prepared by a third party; however, he refused to reveal their details.
He also refused to identify all of his staff and became agitated when asked about customer payments made into Stewart's account; he walked out of the interview.
When questioned, Stewart said Williams was responsible for preparing the tax returns. She admitted owning the diary and making its entries.
IRD investigators also interviewed staff. One admitted that she was paid "under the table", while others mentioned the names of people for whom PAYE tax returns had never been filed.
Williams and Stewart were convicted by Judge Chris McGuire and remanded on bail for sentencing next month.
The couple face a maximum of five years in prison or a $50,000 fine on each charge.
Stewart Drake International Ltd was put into liquidation in September last year.
