If you have damage to the car which might detract from the GCB it might be worth either getting the damage repaired yourself if under £100 or if over making an insurance claim as if paying out £100 means you get your £650 back its worth it.
Had a family memver that managed to poke a hole in a rear light told no GCB if it goes back that way £250 fog a light assbly or £100 insurance excess. So they made an insurance claim, garage bought a new light cluster out & fitted in her driveway next day car went back & got the full GCB