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I have a simmilar story - I was working for now-defunct Carillion, we were doing a load of new build work on a north london military base. They couldn't / wouldn't provide any ug services drawings for security reasons, so every time the excavators / groundworkers hit a cable or pipe, we had to tell the base, they made everyone go away and their own Royal Engineers teams erect a massive shield around it to hide the action, fixed and / or reburied it but in secret location elsewhere.
The company I worked for at the time was told by the principle contractor who was told by the client that they were required for all work onsite that involved drilling into walls or floors. This was after someone accidentally knocked out an air traffic control server room with a services strike, luckily because it was a critical system there were/are multiple redundancies. It did however cause a certain amount of chaos.