National grid will still distribute energy (this might not be the case in local communities). But platform will provide you an opportunity to buy electricity directly from producer. As you would buy flour directly from miller instead from Tesco/Aldi/etc
So, you're hoping that National Grid will adopt this? Those are some pretty big plans.
Otherwise, if your power came form National Grid then you can't choose who it came from or even know who it came from. In order to have a decentralized exchange of power you'd need your own network with this software.
There are certain goal for reduction of carbon footprint and the only way to meet those is to accept anyone to the grid that is willing to produce green energy. And where energy sector is liberalized grid operator has to accept everyone