4. Where an employer or a self-employed person requires any work in relation to a gas fitting to be carried out at any place of work under his control or where an employer or self-employed person has control to any extent of work in relation to a gas fitting, he shall take reasonable steps to ensure that the person undertaking that work is, or is employed by, a member of a class of persons approved by the Health and Safety Executive under regulation 3(3) above.