The customer wants an extension.
So, I met the builder and the plumber at the customers house to finalise the quote when the customer asked me and the plumber "Can you fit water and electricity meters so that I do not have to pay for the water and electricity used by the building works?". At first I thought he could claim something back by seperate useage, but it turns out he want to bill the builder for water and electricity usage.
I have no idea how much electricity will be used by the builder and all the other people on site. But I'll bet it is less than the £100 I want to supply and install a meter and a temporary socket.