Have you been overcharged on your gas bill? It would appear that some Gas suppliers have not converted some charges over when the meter was changed from imperial to metric standards.

It is estimated that gas suppliers have overcharged customers by approximately £1.7 billion.

Check your gas bill? Does your bill have an (M) on it or (ft^3) M means that your bill is charging for metric readings, while the ft^3 reading is the imperial measure and needs to be converted after the readings are made.
If you were on an imperial meter, then had a Metric one installed at a later date - is your supplier sending you bills with M on them or ft^3. If the bill is marked for M, it should be OK, but if your bill is marked with ft^3 when you have a Metric meter - you could be overcharged.
I opted for a pay as you go meter - at least I know where I stand on costs.