The wikipedia bit:

I Believe in Father Christmas" is a song by English musician Greg Lake with lyrics by Peter Sinfield. Although it is often categorised as a Christmas song, this was not Lake's intention. He said that he wrote the song in protest at the commercialisation of Christmas. Sinfield, however, said that the words are about a loss of innocence and childhood belief. Released in 1975, the song reached number 2 on the UK Singles Chart,

The number 1 at that time was Bohemian Rapsodie.