if everyone had a smart meter, there would be a saving in meter reading costs which would be shared by all customers
That's not the way they are planning it. Smart meters certainly reduce the cost of reading, and that saving is going to be passed on to those people who have them, but people who remain with old meters aren't going to see any saving, quite the reverse in fact.
Expect to see a separately itemised reading charge on your bill if you stick with an old meter. Also expect not to be able to take advantage of new Time of Use / Demand Response tariffs as and when they come onto the market.
