The gas meter and the electric meter both talk to the communications hub, which handles the link to your IHD and the uplink to the supplier(s). The communications hub is physically attached to, and dependent on, the electricity meter.
If you don’t have a smart electricity meter, then installing a smart gas meter wont work because there’s no communications hub. If you have a smart gas meter installed anyway, then it can’t be fully commissioned. Once you then go ahead and get the electricity meter installed, it’s not clear who’s job it is at that point to deal with commissioning the gas meter.
Likewise, if you have your smart electricity meter installed first, and then later have your other supplier install a smart gas meter, it’s not clear how they’re supposed to handle dealing with the electricity meter + communications hub in order to get their new gas meter commissioned.
I’m sure there must be a way around this problem, but given all the other problems getting smart meters to work if it were me I’d definitely make sure I had one supplier handling the dual fuel installation. You could then split your service between two suppliers, and hopefully they can both get the data they need from the DCC independently.