Caught a tiny bit of a call-in on energy suppliers on the car radio just now...
I seems there's a problem with smart meters if you want to switch supplier - not all suppliers can use all smart meters, and you might find that your new supplier cannot use the smart meter you have.
This will require you to reverse the switch, or to buy a new meter, both being options that cost you (£60 was mentioned).
Energy regulator is aware of the problem and is trying to get the suppliers to allow a free switch back when this happens, but suppliers don't currently to do that.
I only heard the tail-end of the section on this issue. There might have been more to it.