(1) An employer shall not employ an employee to do any work in a relevant period during which the employee has done work for another employer, except where the aggregate of the periods for which such an employee does work for each of such employers respectively in that relevant period does not exceed the period for which that employee could, lawfully under this Act or the Activities of Doctors in Training Regulations, be employed to do work for one employer in that relevant period.

(2) In subsection (1) ''relevant period'' means a period of -

(a) 24 hours,

(b) 7 days, or

(c) 12 months.

(3) Whenever an employer employs an employee in contravention of subsection (1), the employer and the employee shall each be guilty of an offence.

(4) Where an employer is prosecuted for an offence under this section it shall be a good defence for him or her to prove -