Not all documents need a signature by a doctor, for example passport applications. You can ask another person in a position of trust to sign such documents free of charge.
If you have several forms requiring completion, present them all at once and ask your GP if he or she is prepared to complete them at the same time to speed up the process.
Do not expect your GP to process forms overnight. Urgent requests may mean that a doctor has to make special arrangements to process the form quickly, and this will cost more.
