During his investigations into the
Borley Rectory case, over a period of years, Underwood traced and personally interviewed almost every living person who had been connected with what the press had dubbed the 'most haunted house in England'. He built up a volume of correspondence with paranormal investigator
Harry Price and after Price's death, Paul Tabori would become literary executor of the Harry Price Estate, with whom Underwood worked to publish all his research into Borley. Price had written and published two books about Borley,
The Most Haunted House in England (1940), and
The End of Borley Rectory (1946), from which Underwood 'compile[d] a really comprehensive index of the combined volumes'. Underwood's published work changed the field of literature on the paranormal. For example, his much imitated
Gazetteer of British Ghosts (1971) and
Haunted London (1973) - previously unheard of comprehensive and well-researched surveys (or geographical dictionaries or
gazetteers) - which, through their encyclopaedic thoroughness, imparted authority to Underwood as an author on the subject of
ghost hunting to which he dedicated his life. They also encouraged others to use them as resources to use to visit for themselves the sites he investigated. Underwood came to be known as a 'veteran psychical researcher ... representing the middle-ground between scepticism and uncritical belief'; the 'Sherlock Holmes of psychical research' - as
Dame Jean Conan Doyle would say (when introducing him). In their book
Ghosts of Borley (1973), Underwood and Paul Tabori wrote that they believed "some of the phenomena were genuine" at the
Borley Rectory. The researcher
Trevor H. Hall criticized Tabori and Underwood for
selective reporting. According to Hall, the alleged paranormal phenomena from the rectory were the result of natural causes, such as noises produced by
rats or flying bats, pranks by local village boys throwing stones at the house, or
tramps trying to keep warm by lighting small
fires in the rectory. Underwood was a long-standing member of the
Society for Psychical Research. For some years Underwood was the Honorary Librarian of the
Constitutional Club and the
Savage Club, where he was a former Member of the Qualifications Committee. In 1976 a bust of Underwood was sculpted by Patricia Finch, winner of the gold medal for Sculpture in
Venice (it currently resides with the Savage Club). In 2018 a website was published by his grandson Adam Underwood chronicling his life and work. ==Ghost Club Society==