A 48-year-old patient, who smokes 15 cigarettes per day, presents for a routine examination.
The Basic Periodontal Examination (BPE) reveals a highest score of 4 in one sextant.
According to the 2017 Classification of Periodontal and Peri-Implant Diseases and Conditions as implemented by the British Society of Periodontology (BSP), what would be the most appropriate initial Grade to assign to this patient?