4. In Article 2(4) of the [1978 NI 9.] Health and Safety at Work (Northern Ireland) Order 1978 (meaning of work and at work) in sub-paragraph (b) the word “and” shall be omitted and after that sub-paragraph there shall be inserted the following sub-paragraph—
“(bb)a person holding the office of constable is at work throughout the time when he is on duty, but not otherwise; and” .