Well, that was a surprise. I saw the title and instantly hit the record button, although I'd never heard of it. I assumed it was a documentary. I also assumed it would suck, but I couldn't resist.
Turns out it was an episode of the British television series Urban Myths. The Sex Pistols vs. Bill Grundy was the final episode of the second season (there have been three so far). Lo and behold, it wasn't a documentary. According to the infallible Wikipedia, "Urban Myths is a British biographical comedy drama television series ... Each episode featured a story surrounding popular culture which may or may not be true". In the episode in question, actors portrayed the various actual people who participated in the infamous Bill Grundy affair. The only real thing was the snippets of actual Sex Pistols songs on the soundtrack.
The interview, when it comes (the episode is 22 minutes long, so there is a lot of backstage stuff), looks accurate. Clearly, someone spent some time on YouTube watching the actual event. The costumes are right, and the actors look pretty right, too ... at least they resemble their real-life counterparts. But it's all very pointless. If you're dying to see this (and haven't seen it already a hundred times), here it is. Accept no substitutes: