Director joint liability arises where company liquidation leaves unpaid tax, unless non-recovery isn't due to gross neglect or breach. Upon a company's winding up the appointed liquidator must notify the Commissioner within thirty days; the Commissioner must then, after inquiry, notify within three months the amount deemed sufficient to cover tax, interest or penalty. If a private company's assessed tax, interest or penalty cannot be recovered, every person who was a director during the relevant period is jointly and severally liable for that liability unless he proves to the Commissioner that non-recovery was not due to gross neglect, misfeasance or breach of duty.