The standard format for an electricity supply number is:
The top line of the supply number contains information about whether you are a domestic or business consumer, and which tariff you are on. It will therefore change as you change your supply details.
The bottom line of the supply number contains information about the local electricity distribution company responsible for maintaining the cables and wires carrying electricity into your home, plus a unique reference number to identify the meter in your property. The bottom line of information will not change when you switch supplier.