You need to prove that you have a valid GMC licence to practice.
👉 Find and scan GMC full registration certificate
This is the blue hard copy certificate you received when you first registered with the GMC.
If you can't find it, let the locum agency know. They may let you sign a declaration to say you no longer have access to it.
👉 Send GMC annual retention letter
This is also called your Certificate of Proof of Entry
You can view and print this directly from your GMC Online account. Login (go here) and from the left hand menu choose "My Registration", then select "View certificate".
Send this over to the locum agency.