There have been several debates on what was the first and original “Mockumentary” normal prompted by me getting annoyed 
when this is credited to the office.
This is my view so far 1984 “This is Spinal Tap” (film)
1985 “Victoria Wood As Seen On TV” (sketch)
1997 “Operation Good Guys” (sitcom)
Can anyone beat that? 
Barry
Looking at http://en.wikipedia.org/wiki/Mockumentary, there's quite a few as far back as the early 60s at least.
Operation Good Guys is often mentioned on these pages, but one thing not commented on is there disasterous decision to include a laughter track on the second and third series. It really did feel wrong.
I bought the complete set and was devastated (literaly) by the laugh track on the last two series. If I want to be told when to applaude and roar, I'd have become a sealion.
I thought the "Where Are They Now" extra on the Operation Good Guys DVD was also very poor. Mind you, I only paid £9.99 for it so I can't complain.