Damaged gas meter cover

A certain member of my family has damaged the surface mounted gas meter cover box mounted on the side of the house reversing a car off the drive. It's one of those old white composite ones with a drop down door and the cover is quite badly damged at one corner. I'm pretty sure the meter inside is undusturbed - at least I can't smell gas! The backplate still seems securely fastened to the wall. Can you buy these at a builders merchants (Wickes, B&Q, etc) and fit these yourself or is there some obligation to contact the meter provider (British Gas) or the gas supplier (in my case, Powergen). If, on further inspection, I need to verify the meter/supply is undamaged who should I call and is there likely to be a charge for this. Many thanks.