Putting us on mains water did not need access to the property but as you say, they will need access for the switch over to mains electricity...On R3, they came early on the morning and dashed between properties. the whole lot were done in a day..there was a group of workmen fitting the outside meters and another group fitting the isolating switches etc., inside...and if access cannot be gained, there is quite a high charge for getting them back later.