You can base it on the wholesale price, great if you have battery storage
https://octopus.energy/smart/agile/
Or just an overnight rate
https://octopus.energy/smart/intelligent-octopus-go/
Again if you put in a £5k 10kWh battery you are golden, as you put 8kWh into your car and 8kWh into your battery every night, dropping your electric cost to £38 a month (plus the standing charge, which is far higher)