I just sent a post to tpin saying I'd heard it was Bill Phillips, but I'm writing to correct myself. I checked a book I have, "The Beatles Recording Sessions - The Official Abbey Road Studio Session Notes, 1962 to 1970," by Mark Lewisohn. It's published by Harmony Books, a division of Crown Publishers, Inc., 225 Park Avenue South, New York, New York 10003 ISBN 0-517-57066-1 (1988) (Reprinted in 1989).
(page 93) "Penny Lane still needed the finishing touch. Paul McCartney realised what it was when he sat watching the second of a five-part, late-night BBC2 television series 'Masterworks' at home on the Wednesday evening of 11 January."
"He saw me playing Bach's Brandenburg Concerto Number 2 in F Major with the English Chamber Orchestra from Guildford Cathedral," remembers David Mason, recruited for the Beatles session . . ." "The next morning I got a call and a few days later I went along to the studio. I took nine trumpets along and we tried various things, by a process of elimination settling on the B-flat piccolo trumpet." "We spent three hours working it out," says Mason. "Paul sang the parts he wanted, George Martin wrote them out, I tried them. But the actual recording was done quite quickly. They were jolly high notes, quite taxing, but with the tapes rolling we did two takes as overdubs on top of the existing song. I read in books that the trumpet sound was later speeded up but that isn't true because I can still play those same notes on the instrument along with the record."
"I was in the New Philharmonia then, now known simply as the Philharmonia, and still am. I've spent a lifetime playing with top orchestras yet I'm most famous for playing on 'Penny Lane'!"
(Please see the top of this post for information re: where this was borrowed from, and where the book can be found, should anyone want to purchase one.)