The beginning of this song was based on two stories John Lennon read in the Daily Mail newspaper: Guinness heir Tara Browne dying when he smashed his lotus into a parked van, and an article in the UK Daily Express in early 1967 which told of how the Blackburn Roads Surveyor had counted 4000 holes in the roads of Blackburn and commented that the volume of material needed to fill them in was enough to fill the Albert Hall. Lennon took some liberties with the Tara Browne story - he changed it so he “Blew his mind out in the car.”
John Lennon stated this regarding the article about Tara Browne: “I didn’t copy the accident. Tara didn’t blow his mind out. But it was in my mind when I was writing that verse.” At the time, Paul didn’t realize the reference was to Tara. He thought it was about a “stoned politician.” The article regarding the “4000 holes in Blackburn, Lancashire” was taken from the UK Daily Express, January 17, 1967 in a column called “Far And Near.”
John’s friend Terry Doran was the one who completed John’s line “Now they know how many holes it takes to fill...” Terry told him “fill the Albert Hall, John.”
http://www.songfacts.com/detail.php?id=129
Darn. I always thought they were talking about John being dead there, or being the walrus...or something!