short film has come to light (thanks,
Jim) in which organist John Gosling asserts that he was planning
to join Procol Harum or Squeeze at the time he signed up with the Kinks.
Watch it (the bit starting at 4m 16s, anyway) with a pinch of salt. Gosling joined The Kinks in 1970, but Squeeze didn't even form until 1974 and Jools Holland, whom he cites, first left that band in about 1980.
If there's any chronological veracity to Gosling's claim, the Procol vacancy he was contemplating would have been occasioned by the departure of their early organist Matthew Fisher. Fisher's replacement, Chris Copping, first played with Procol at the end of 1969 (bass only, not organ)
More reliable memories from a non-Procoler come in this illuminating account of a top-flight musician's encounter with the band, and his reactions to their music: it offers very cogent opinions about 'classical rock' which any visitor to this website will probably enjoy reading.