yep, the daily telegraph ran a competition for potential new union jack designs, as whales isn't included. Several anime suggestions, but the overall winner was that one. The designer was VERY upfront about where it came from, qouting lines from the series several times. Twas Gurren Lagann.
Exactly how it ended up on that tank is unknown, except to say Gurren Lagann has acheived full blown meme status. An anime news networks article on it is
here and a good vidclip
here.
I'm a little surprised Rhys hasn't noticed this thread yet
