@des is bang on!
An EV tariff is a a 2 rate tariff, that works in basically the same way as Economy 7 does today, where a block of off peak hours often overnight at a cheap kW/h rate and a slightly more expensive kW/h day rate, than if you were on a standard 1 rate tariff. Like economy 7 there is one standing charge.
It use to be (and where some are getting confused) Economy 7, had the older RTS meters, which use to have 2 sets of readings (day/night). However, they should have been replaced with “Smart” meters, which are able to differentiate between on/off peak hours.