Best answer by Nancy_OVO
I've added some tags to this so other users can find information they might need.
A company called Secure make the models of smart meters that we use. We pay Secure for the meters and install them. We are responsible for the meters and therefore take ownership of the charges. If you were to switch supplier, the new company would become responsible for the meter as soon as you transfer over to them.
The DNO (Distribution Network Operator) is responsible for the maintenance of the grid up to the point of the pysical meter. This is where their responsibilty ends. Our DC (Data Collector) collate and verify readings for us, but we need them to do this for both traditional and smart meters, so they're not responsibile for smart meters specifically.
I hope this has answered your questions, let me know if you have any more below!