Hi Graham,
Yes I know what you mean about the gas meter box, they can look awful on the out side of a period house.
However you will notice on all new builds the meters for both electric & gas are always external some are not very noticeable because they are semi underground in a brown box a far less intrusive solution.
This has two main effects (1) the meter reader can do his job without disturbing the house owner. (2) It limits the right of access into your home by the relevant authorities i.e. the gas emergency service.
The meter always remains the property of the gas supplier and therefore if there is a problem they along with a member of Her Majesties Constabulary can if necessary force access to said meter. Having an external meter denies them this right of access.
Colin H.