(1) This section applies to an employee whose contract of employment operates to require the employee to make himself or herself available to work for the employer in a week -

(a) a certain number of hours ("the contract hours''),

(b) as and when the employer requires him or her to do so, or

(c) both a certain number of hours and otherwise as and when the employer requires him or her to do so,

and the requirement is not one that is held to arise by virtue only of the fact, if such be the case, of the employer having engaged the employee to do work of a casual nature for him or her on occasions prior to that week (whether or not the number of those occasions or the circumstances otherwise touching the engagement of the employee are such as to give rise to a reasonable expectation on his or her part that he or she would be required by the employer to do work for the employer in that week).

(2) In a contract for a certain number of hours of work referred to in paragraphs (a) and (c) of subsection (1), the number of hours concerned shall be greater than zero.

(3) Notwithstanding subsection (1), subsection (2) shall not apply to -

(a) work done in emergency circumstances, or