EDIT: Or possibly just 83.5 . . . see artiofab's comment below.
Since 1849, two archival copies of every U.K. bill have been printed on sheets of high-quality vellum. One is sent to Victoria Tower, while the other goes to the Kew National Archives. Vellum lasts a long time, far longer than archival paper, and with the expectation that the U.K. will live on for thousands of years it remains the storage media of choice.
(This is a substantial improvement on the previous system, where bills were written on continuous parchment scrolls . . . the Roll of Parliament containing an 1821 tax bill was a quarter of a mile long and took two men a full day to roll up.)
Vellum, however, is an animal skin parchment, and the animal is usually a goat. And naturally, the longer the bill, the more goats it takes to produce the vellum for the legally-required copies.
Enter HS2, the proposed high-speed rail line connecting London to Birmingham. At 49,814 pages, its bill is the longest bill ever to come before the U.K. Parliament. And once it's signed into law, printing all those pages (twice!) is going to take a lot of goats. Six thousand goats.
(I know, the headline gave it away.)
Ian Mansfield came up with this approximation, in a post to his blog, IanVisits. And while he clarifies that 6,000 is just a rough estimate . . . even if he's off by a couple thousand, that's still a whole lot of goats!
Image via Wikimedia Commons, slightly modified.