How much does a doctor's note normally cost?

I'm just wondering cos I need my GP to write me a note before my 18th birthday so i can have my gender change to female on my passport at 18.



I can't wat.



How much does a Doctor's note generally cost anyway? Cos my mum said you have to pay.



Btw, i've checked already that my GP is eligible to write that note, but i do need to prove to him that the change to my passport will be permanent.



Btw, also i live in the UK.How much does a doctor's note normally cost?
There is no fixed fee for such a service. The payment requested would be entirely at the doctors discretion.