As a very rough guide, a kWh of electrical energy costs around 10 pence, in comparison a kWh of gas energy costs around 4 pence. You claim to be using around £3 of gas/day – that works out at around 75kWh of energy, or a continuous 3kW per hour (averaged over 24 hours).
Given as samuelcat says, you will be paying a slight premium on my prices (being on a prepay meter) – all things considered, I would say that heating a 3 bedroom house with a continuous 3kW electric fire on, is not bad.
It just goes to show how much energy costs, bear in mind that £3/day is likely to be your maximum energy usage/day (due to the cold weather) and that during the summer months it is likely to be significantly less than £1/day.