You need to look at the thread A taste of things to come? - UK smart meter data access
Somewhere in there I think I’ve seen something about who is allowed access to the encryption keys that the Smart Meter uses to send the data. I got the impression that they are closely guarded, though you might be able to buy your own meter with its own keys.
As far as I know (bearing in mind I’m an electrical engineer, not a gas man), as long as your installation uses approved fittings and is done by an approved person, you can have what you like. But you really need to speak with whoever is likely to do the installation and knows the regulations, and I suspect it’s likely the installer will have to buy the meter, as they are likely to refuse to sell it directly to you.