14. If the promoter gives notice in writing to the specified undertaker that it desires to carry out any part of any work to which this paragraph applies, such work, instead of being carried out by the specified undertaker, may be carried out by the promoter with the prior written consent of the specified undertaker (which must not be unreasonably withheld and is subject to any such conditions as are reasonable and proper to protect the apparatus) in accordance with plans and in a position agreed between the specified undertaker and the promoter or, in default of agreement, determined by arbitration, without unnecessary delay under the superintendence (if given) and to the reasonable satisfaction of the specified undertaker.