Section 67(1) of the New Roads and Street Works Act 1991 (“the 1991 Act”) places a duty on the undertaker, subject to exceptions, to secure that the execution of street works involving breaking up the street, or any sewer, drain or tunnel under it, or tunnelling or boring under the street, is supervised by a person having a prescribed qualification as a supervisor. Section 67(2) of the 1991 Act requires at least one trained operative to be on site at all times where an undertaker executes street works involving breaking up or opening the street or any sewer, drain or tunnel under it, or tunnelling or boring under the street.