With his eldest three children, he returned to England and participated in geological and natural history studies at the British Museum and the University of London.
Newcombe began to study the botany of North America and made many trips to Haida Gwaii (formerly the Queen Charlotte Islands) by boat.
In the process he became very interested in the Haida and started to collect their artifacts to "preserve" them from, what was then thought to be, the impending demise of the native culture.
In 1897, George Amos Dorsey traveled with him in an effort to collect Haida artifacts for the Field Columbian Museum in Chicago.
In 1904, he went with six Vancouver Island First Nations people and their medicine man to the World's Fair held in St. Louis to show their crafts and culture.
Much of his work, including collection of plants, mollusks, fossils, aboriginal artifacts and information, was done with the help of his youngest surviving son, William Henry Arnold Newcombe (1884-1960).