something doesn't sound quite right there to me, that works out to about 1400 pounds a year, i would have said an average price for your size house would be about 600 a year.
i have heard a lot of people complain that they have been overcharged when using card meters and have had real problems getting the money refunded. if its possible i would switch to a normal gas meter and pay by direct debit which is cheaper. look at changing to a cheper gas supplier. perhaps get your gas appliances serviced as they could be set to the wrong burner pressure and using too much gas. if you've not got a room thermostat for your heating then get one installed and then turn the heating down as low as is still comfortable. its often cheaper to leave the heating on all day at a slightly lower temp as the boiler uses most gas when heating up from cold rather than just maintaining a constant temp.