Volume is the main driver, and it changes the price more than anything else.
Take two patients booking a consultation on the same day. One has a slightly recessed chin and wants subtle softening. That typically needs 1ml, around £300. The other has a genuinely weak chin affecting their whole facial profile and wants real structural change. That can mean 3ml or 4ml, £700 to £900.
Same treatment, same practitioner, a £600 difference, purely down to how much correction the anatomy actually needs.
Practitioner expertise is the second major factor. The chin sits close to the mentalis muscle and several small nerves, and judging the right proportion relative to the nose and lips takes real experience. That expertise is priced in for good reason.
Location matters too. Central London, and Mayfair or Harley Street specifically, runs higher than regional UK clinics, reflecting both overheads and a concentration of specialist injectors.