(4) When signifying his approval of the plans the engineer may specify any protective works  (whether temporary or permanent) which in the engineer’s opinion must be carried out before the  commencement of the construction of a specified work to ensure the safety or stability of railway  property or the continuation of safe and efficient operation of the railways of Network Rail or the  services of operators using those railways (including any relocation, decommissioning and  removal of works, apparatus and equipment necessitated by a specified work and the comfort and  safety of passengers who may be affected by the specified works), and such protective works as  may be reasonably necessary for those purposes must be constructed by Network Rail or by the  undertaker, if Network Rail so desires, and such protective works must be carried out at the  expense of the undertaker in either case without unnecessary delay and the undertaker must not  commence the construction of the specified works until the engineer has notified the undertaker  that the protective works have been completed to his reasonable satisfaction.  36. —(1) Any specified work and any protective works to be constructed by virtue of paragraph  35(4) must, when commenced, be constructed—  (2) If any damage to railway property or any such interference or obstruction is caused by the  carrying out of, or in consequence of the construction of a specified work or a protective work, the  undertaker must, regardless any such approval, make good such damage and must pay to Network  Rail all reasonable expenses to which Network Rail may be put and compensation for any loss  which it may sustain by reason of any such damage, interference or obstruction.  (3) Nothing in this Part of this Schedule imposes any liability on the undertaker with respect to  any damage, costs, expenses or loss attributable to the negligence of Network Rail or its servants,  contractors or agents or any liability on Network Rail with respect to any damage, costs, expenses  or loss attributable to the negligence of the undertaker or its servants, contractors or agents.  38.  Network Rail must at all times afford reasonable facilities to the undertaker and its agents  for access to any works carried out by Network Rail under this Part of this Schedule during their  construction and must supply the undertaker with such information as it may reasonably require  with regard to such works or the method of constructing them.  37.  The undertaker must—  39. —(1) If any permanent or temporary alterations or additions to railway property are  reasonably necessary in consequence of the construction of a specified work or a protective work,  or during a period of 24 months after the completion of that work in order to ensure the safety of  railway property or the continued safe operation of the railways of Network Rail, such alterations  and additions may be carried out by Network Rail and if Network Rail gives to the undertaker  reasonable notice of its intention to carry out such alterations or additions (which must be  specified in the notice), the undertaker must pay to Network Rail the reasonable cost of those  alterations or additions including, in respect of any such alterations and additions as are to be  permanent, a capitalised sum representing the increase of the costs which may be expected to be  reasonably incurred by Network Rail in maintaining, working and, when necessary, renewing any  such alterations or additions.  136 (b) supply the engineer with all such information as the engineer may reasonably require with  regard to a specified work or a protective work or the method of constructing it.  (a) at all times afford reasonable facilities to the engineer for access to a specified work or a  protective work during its construction; and  (a) without unnecessary delay in accordance with the plans approved or deemed to have been  approved or settled under paragraph 35;  (b) under the supervision (where appropriate and if given) and to the reasonable satisfaction  of the engineer;  (c) in such manner as to cause as little damage as is possible to railway property; and  (d) so far as is reasonably practicable, so as not to interfere with or obstruct the free,  uninterrupted and safe use of any railway of Network Rail or the traffic on it and the use  by passengers of railway property. 