Salaries chargeability: taxable when due, paid or allowed, and arrears taxable if not previously charged. Salaries are chargeable where remuneration is due from an employer, where salary is paid or allowed even if not yet due, and where arrears are paid or allowed in the tax year if not previously taxed; a former employer is included within the definition of employer. Advance salary included once shall not be taxed again when it becomes due. Payments to a partner by a firm described as salary, bonus, commission or remuneration are not regarded as salary for this head.