Campbell Connelly, a music publishing company established by English songwriters Jimmy Campbell and Reg Connelly was among the first ones to settle in Denmark Street.

They moved their office to Denmark Street in 1926, and formally established the music publishing firm Campbell Connelly in 1929. Here, they wrote their famous song "If I Had You" with composer Ted Shapiro. The song was later recorded by Judy Garland, Nat King Cole, Frank Sinatra, and many others. They had further success in 1931 with "Goodnight Sweetheart," written with composer Ray Noble and recorded by Guy Lombardo, Al Bowlly and Rudy Vallee among others.

In 1952, the New Musical Express was founded here at No. 5. For those who do not know, New Musical Express (NME) is a British music, film and culture website and brand. Founded as a newspaper the NME became a popular magazine and later - an online brand which includes radio stations.  

Read more https://www.nme.com/
Other sources: Wikipedia