Sackville Street is part of the Savile Row tailoring area in Mayfair in London. Many people are familiar with the idea of the high quality tailoring in Savile Row. "Savile Row", in terms of tailors, is traditionally regarded as including Savile Row itself and a few of the adjoining streets, such as Sackville Street.
Nichols (Sir Laurence Olivier), and later Roberts (Adolphe Menjou), quotes "Oh, to be in England now that April's there", which is from "Home-Thoughts from Abroad" by Robert Browning (1812-89).
Although the score is credited to Victor Schertzinger and Max Steiner, in fact Steiner did not write any music for this movie, serving only as Musical Director.
The five thousand pounds sterling blackmail would equal about twenty-two thousand six hundred eighty U.S. dollars at the time, or approximately three hundred fifty thousand U.S. dollars in 2017.