Hi
The meter using as much as £8 per day seems very high, but the chance of the meter being faulty is extremely low.
As this is a prepayment gas meter the meter settings may hold the answer to why so much money is being taken. The meter may have a debt set on it from the previous owner/tenant and when you top up this money is still being collected.
I recommend contacting British Gas and speaking with their prepayment department, you can either take the meter settings before hand or ask them to talk you through this process (there are around 20 different displays) note down all the information and give it to British Gas.
They should be able to then check you are not paying a debt that isn't yours and that the meter is calibrated to the correct prices. If this does not highlight any discrepencies tell them you are still concerned and ask them to go through your consumption with you.
Swapping the meter is a good idea as you will then have a wider choice of tariffs and payment methods, however some suppliers won't change the meter unless the circumstances suit them, worth discussing anyway.
First and foremost establish why the charges are high as changing the meter might not be the answer to this.
Brian
Employee of E.ON