Subject to the provisions of this Order, in the construction or execution of the renewal, replacement, extension or alteration of the works the Authority may deviate laterally from the lines or situations shown on the deposited plans and sections to any extent not exceeding the limits of deviation and may deviate vertically from the levels of the works shown on the deposited plans and sections to any extent not exceeding 3 metres upwards and to such extent downwards as may be necessary or convenient.