Spinal Tap is pretty much a rip-off of a mockumentary called
Bad News Tour, starring British comedians Rik Mayall, Ade Edmondson, Nigel Planer, and a few others (there's also a sequel called
More Bad News). I think it's actually funnier than
Spinal Tap, but then I'm a fan of Mayall and Edmondson.
Here's a clip of a TV appearance they did:
Excerpt from
Bad News Tour - "Warriors of Genghis Khan":
Excerpt from
More Bad News -