Electrical Connections

I have an existing wall mounted socket that I want to use for connection of built in dishwasher. I envisage my kitchen supplier fitting the kitchen leaving a hole in the back of the cupboard adjacent the dishwasher unit so that I can access this socket and plug my dishwasher in. The firm supplying the kitchen imply that their fitter needs to fit a socket on the inside of the cabinet with subsequent testing/certification of any electrical work. What are my options with this.
TIA