Peer to peer energy trading in the UK is not yet possible. This is because it is not possible for consumers to have more than one contact with an electricity supplier. There are trials going on to work out how systems could operate and diffident business models etc but fundamentally regulations need to change before it can be rolled out. More info if you're interested: https://www.solar-trade.org.uk/trading-sunlight-prospects-for-peer-to-peer-energy-trading/