People looking for a classical concert in London are truly spoilt for choice. The city boasts five major orchestras and regularly hosts many others; several venues for chamber music and smaller-scale orchestral performances; choral works are frequently played in the main concert halls as well as in churches, and there are two major opera houses.
The Barbican Centre where the well known London Symphony Orchestra perform (and the BBC Symphony Orchestra) as well as the Southbank Centre (where you find both the Royal Festival Hall and Queen Elizabeth Hall,) home of the Philharmonia and London Philharmonic Orchestra vie for the title of London's premier hall for orchestral concerts. Cadogan Hall, near Sloane Square, is the main home of the Royal Philharmonic Orchestra, which also performs music outside the standard classical repertoire. In summer, the attention shifts to the BBC Proms festival at Kensington's Royal Albert Hall, which hosts a dazzling array of visiting Orchestras as well as the BBC's own performing groups.
The Wigmore Hall in Marylebone, is the capital's home of instrumental and chamber music. In addition, there are many other venues for smaller scale events, joined recently by the newly built King's Place, a development near King's Cross station which houses the London Chamber Music Series. London has several specialist orchestras such as the Orchestra of the Age of Enlightenment (specialising in baroque and early music), and the London Sinfonietta, which plays 20th and 21st century works.
London has two internationally acclaimed opera companies: the Royal Opera (which performs at the Royal Opera House, Covent Garden), and the English National Opera, which performs at the London Coliseum and always sings opera in English. Less known is the fact that there are several smaller opera companies such as Hampstead Garden Opera, who perform in smaller venues with tickets suitable for considerably smaller budgets!These are some great concerts also to be found at the music colleges: the Royal Academy of Music and the Royal College both have events which showcase their students: these are often of very high quality.
There are dozens of other venues not listed above. If you're a music fan visiting the capital and looking for a classical music concert, you'd be hard pressed to pick a day when nothing's playing, and if you live in London, you have an overwhelming selection of orchestras, conductors and pieces of music in different styles from different composers. The main danger is to your bank balance!