I thought the whole point in Agas was that they run continuously? Which makes sense if they're also providing space heating, and you don't have a more efficient alternative.
Maybe the electric ones are built more like a normal cooker for posh people, with insulation and knobs to twiddle instead of loads of thermal mass?
ETA: Apparently not. They still do the ticking over continuously heating the room thing, but you can turn the hob bit on and off to save energy. 220kWh per week, thobut! That's like running a car 
When we got rid of our oil-fired Aga 10+ years ago, we reckoned it was costing us a fiver a day to fuel. It kept the kitchen nicely warm in the winter (which was great at weekends, but felt like a waste when we were both at work), and made wonderful toast.
We have a oil-fired (stanley) for central heating.
Come summer, we turn it off entirely. If it's cool in the evening, we light a fire in the living room.
When firing, it burns 6l of oil an hour. However, it doesn't fire continuously, and, once hot, acts as a heat store for most of the day (there is quite a lot of energy stored in 360kg of steel).
