The son of the Rector of the village, later to be consecrated as the first Bishop of Dunedin in New Zealand, Jenner heard his father and a guest discussing the Cornish language and this sparked his fascination with Celtic languages.

In 1877, he discovered, at the British Museum, forty-two lines of a medieval play written in Cornish around the year 1450.

In 1904, he published ‘A Handbook of the Cornish Language’, which sparked a revival of interest in the language spoken in West Cornwall in the 18th century.  At its publication, Jenner observed that ‘There has never been a time when there has been no person in Cornwall without a knowledge of the Cornish language … The reason why a Cornishman should learn Cornish, the outward and audible sign of his separate nationality, is sentimental, and not in the least practical, and if everything sentimental were banished from it, the world would not be as pleasant a place as it is.’