The Philharmonia Orchestra was founded in 1945 by Walter Legge and is based in London. It was known as New Philharmonia Orchestra between 1964-1976, and returned to the name Philharmonia Orchestra in 1976 (see http://www.philharmonia.co.uk/about/history/).
It is not the non-professional New Philharmonia Orchestra of Massachusetts, founded in 1995 and based in Massachusetts, USA, or the London Philharmonic Orchestra, founded in 1932 by Sir Thomas Beecham.
On 10 March 1964, (Walter) Legge announced that he was going to disband the Philharmonia Orchestra. At a recording session with (conductor Otto) Klemperer, a meeting was convened where those present unanimously agreed that they would not allow the orchestra to be disbanded. Klemperer gave his immediate support, and on 17 March 1964 the members of the orchestra elected their own governing body and adopted the name "New Philharmonia Orchestra". The inaugural concert of the New Philharmonia under its own auspices took place on 27 October 1964. It was a performance of Beethoven's Symphony No. 9, conducted by Klemperer, who was now honorary president of the orchestra. From 1966 until 1972 the chairman of the orchestra was the principal flautist, Gareth Morris. The orchestra gave many more live performances after it became self-governing than it had under Legge's management. It reacquired the rights to the name "Philharmonia Orchestra" in 1977, and has been known by that name since.