Just to agree with andysm - I live in a 5 bed detached with gas for heating,hot water and cooking- my gas usage for the last 6-7 mnths over Winter has averaged out at 2.05 * 100 cu ft per day ( ~ 6 cu m/day) which is ~ £60 per mnth on my tariff with Scot Power.
I suggest that the Transco guy needs to check that you haven't got leaks on your side of the meter - they can do that simply by turning everything in the house off and looking for a pressure drop at the meter.
Have you had your central heating on continuously over the Winter or on a time switch ?? That will have put your usage way up in the very cold weather.