The National Audit Office has been hit with a £97,500 tax bill going back six years after failing to declare the chauffeur-driven car of Sir John Bourn as a taxable benefit.

The tax bill on the £102,500 benefit has been paid out of the NAO budget.

An interest bill of £2,000 will also be met, while the NAO has set aside £6,000 for a penalty payment.

The figures emerge from the remuneration report of the NAO’s 2007/08 accounts, which also disclose that benefits declared by Sir John in relation to his wife’s travel on official trips had been increased by £5,300.

The tax investigation follows revelations in Private Eye magazine over Sir John’s chauffeur-driven car.

Exposure of the tax investigation may prove embarrassing for new auditor general Tim Burr, who sat on the audit committee for the period covered.