This actually happens in Ireland for electric "Storage Heaters", which charge up overnight when electricity is cheap and plentiful, but it's not charged at the usual night rate...

(This may actually no longer be a thing, storage heaters aren't used all that often anymore..)

At least in the mainland UK, I think those kind of plans were replaced by Economy 7/10 tariffs that offer the same rate for all off-peak electricity usage regardless of what it's used for a long time ago.