art 6 Power to deviate
In constructing or maintaining the scheduled work, the undertaker may— (a) deviate laterally from the lines or situations shown on the works plans to the extent of the limits of deviation for that work; and (b) deviate vertically from the levels shown on the sections— (i) to any extent not exceeding 3 metres upwards; or (ii) to any extent downwards as may be found to be necessary or convenient.