Like the RCA Victor and Columbia Symphony Orchestras stateside, the National Philharmonic Orchestra (sometimes "of London," sometimes not) was a nom du disque. The orchestra was popular for its recordings of film scores as well as standard repertoire, and it was led by many of the major conductors of its era.
The National Philharmonic Orchestra grew out of the eponymous RCA Orchestra in London that producer/arranger/conductor Charles Gerhardt (1928-1999) assembled after 1960. Following several years at RCA as an engineer and editor, Gerhardt had been sent to England by George Marek, then the director of Red Seal artists and repertoire, to produce recordings for the Readers Digest label, an RCA ally at the time. For these recordings, Gerhardt engaged Kenneth Wilkerson as his recording engineer and the late Sir Thomas Beecham's Royal Philharmonic. His conductors in the early 1960s included Fritz Reiner, René Leibowitz, Sir John Barbirolli, Jascha Horenstein, Massimo Freccia, and on occasion, Gerhardt himself (whom Toscanini had admired and encouraged in his last years). For projects of lighter music, however, Gerhardt assembled freelance musicians along with players from various London orchestras — always a plenitude in the U.K. capital, where stringent U.S. union restrictions did not apply and salaries were cheaper, with fewer permanent jobs available nationwide. Early on, he called these recording orchestras the London Promenade or the RCASO. In addition to the concert, concerto, and bon-bon repertoire, Gerhardt arranged and conducted ten stereo LPs of film music for the Digest that were released in two volumes. Their quality so impressed Marek's successor, R. Peter Munves, that he commissioned Gerhardt to make an LP of The Classic Film Scores of Erich Wolfgang Korngold for the RCA Red Seal label.
The National Philharmonic, however, ceased to be RCA's or the producer's personal orchestra when Gerhardt replaced Sax as concertmaster, feeling that his playing had deteriorated beyond repair. Thus, Richard Bonynge conducted the NPO extensively for Decca/London recordings of opera and ballet, as well as Riccardo Chailly, Bernard Herrmann, Nicola Rescigno, Gianandrea Gavazzeni, and even Sir Georg Solti. James Levine led operas and recital discs for RCA and Sony. Leopold Stokowski also led the NPO on Sony in final-period recordings until the day before his death in 1977 at the age of 95. After his farewell Wagner recording, Gerhardt retired to California, and from the available evidence, his informal NPO disbanded after 25 years, when the classical market went soft worldwide in the later 1990s, and London players with permanent posts clung to them like becalmed sailors, waiting for a breeze to rescue them from irrelevance as a professional breed.