MPAN (also known as the Meter Point Administration Number) is your electricity meter number. Your supplier may ask for the MPAN or the MPRN (Meter Point Reference Number) when switching to them.
The full MPAN is 21 digits long and should appear on your electricity bill. You can also go to your actual meter, to see what the MPAN is on there - underneath the bar code.
You can contact your local electricity supplier to find out your MPAN if you haven’t got a bill to hand.
You can find out more on how to submit a meter reading here.