Doctor Who: 14 Cool Details Revealed In David Tennant's The End Of Time Part One Commentary
10. Very Few People Were Given The Full Script
There's a lot of secrecy surrounding Doctor Who even with the normal episodes, but when it comes to huge events - like regeneration stories - that secrecy is quadrupled.
Take The End Of Time as an example. Around fifteen minutes into the commentary for Part One, Lyn mentions that the scripts that were released to the cast and crew were missing the final twenty pages of the second episode - so basically, everything from the Doctor's death in the radiation booth, through to the closing credits.
Tennant adds that "very few people" had the full script, and that the readthrough was stopped before the conclusion of Part Two, so as not to spoil the circumstances of the Tenth Doctor's departure.