I have recently started getting a hot sensation running down the outside of my left leg from knee to ankle, like warm water being poured down my leg.

Paresthesia. Paresthesia is a funny feeling usually due to a neurological problem, either peripherally (with the nerve itself) or centrally (in the brain). See a neuroloist for diagnosis and treatment.
Get it evaluated. It is possible that those symptoms are due to a peroneal nerve irritation. It needs to be evaluated.