Storage heaters were originally developed to use electricity produced at night when demand was low which would otherwise have gone to waste, The heat or charge is built up over night and then gradually released during the day. To encourage people to use this heating system the electricity companies discounted the cost of this night time electricity. Originally they gave 7 hours discounted electricity over night, the cheap electricity, being monitored by a separate meter and this was called “Economy 7”. This is still very much the standard in most of England and parts of Scotland.
One problem with this was that much of the heat, produced, giving a cosy house in the morning (often when people didn't need it especially if they were out working and the kids at school) often dispersed by the late afternoon and evenings meaning people were either cold or had to find another method of heating to supplement their storage heaters. There are still about 5 million households in Britain using this system. This was even more of a problem in Scotland with it being that bit colder which led to the introduction of a more flexible solution which was called Total Heating Total Control or THTC.
There are over 150,000 households in Scotland who heat their homes using THTC. This is an improvement on economy 7 as it allows the storage heaters to receive top ups during the day, controlled by a long wave radio signal sent along with Radio 4! The idea is that if the weather looks like it could be particularly cold then the heater will be given a boost as required. However it appears some households under the THTC tariff are set to particular times and come on whether the additional heat is required or not.
A big plus of the THTC system apart from it heating hot water at the cheap rate is that there are effectively TWO supplies of cheap rate electricity one is as mentioned above controlled by others for your storage heaters, the second a constant supply of cheap rate electricity used usually for panel heaters in the bedrooms and a focal point fire in the living room where you can get cheap rate heat instantly when you need it.