They should be on an Economy 7 or a Heatwise tariff and wired separately. You get cheaper electricity for 7 hours during the night from 11 to 6 or 12 to 7.
The heat is stored up while you sleep and released during the day - if you're out at work during the day then this is not necessarily a good idea.
Also if you run your storage heaters during the daytime the cost of electricity through the economy 7 meter is nearly double the normal daytime cost!
Make sure that (a) you have an economy 7 meter and your heaters are connected to it (b) your heaters are on a timed supply to be on only during the cheap rate period (c) you do not operate the meters at the expensive times (d) you don't use them at all when you're going to be out all day (e) you have another form of heating like a fan heater to warm the place quickly when you need to.
A storage heater is very much a plan-ahead type of heating as in switch it on when you go to bed to give you heat next day.
Also contact U-Switch 0800 051 5493 who will tell you which is the best energy supplier for you (free service).
http://www.moneysupermarket.com/gas-and-electricity/economy-7-meters/
Good luck...
Peccavi
April 2013