The supply point number given is used to help energy companies complete the switching process and for the companies that distribute your electricity or gas (local network operators) to identify you.
For electricity this is called a Meter Point Adminstration Number (MPAN) or for gas a Meter Point Reference Number (MPRN).
The first number on the bottom line identifies which network distribution supply region you are in - this is also stated on your bill under the emergency numbers.
You can use Meter Point Administration’s online service Find My Supplier to find details of your gas supplier. They can also provide your Meter Point Reference Number (MPRN).