There's a fine little documentary on Criterion's WITHNAIL & I DVD which features marvelous, priceless home movie footage that Bruce Robinson, the film's writer/director who based the story on his own experiences, shot while living in his squalid flat with his drunken thespian roommates.
The film itself is one of absolute favorites, with Robinson's vivid, hilarious script and a bang-on cast: Richard E. Grant, unforgettable as the titular Withnail (a name, Robinson tells us on the DVD, that came from an older kid from his childhood whose name he slightly mispronounced); the underated Paul McGann as "I" (aka Marwood), Withnail's more level-headed flatmate; Richard Griffiths, as Withnail's wealthy poofter uncle who lends them his cottage (when they go "on holiday by mistake"); and just as memorable, Ralph Brown's [who's had a long career, including the new Pirate Radio] Danny, the mellow drug dealer who looks like he'd be at home in an episode of "The Young Ones" and who says clever things even while his brain is presumably melting ("You have done something to your brain. You have made it high.")
It was a flop when first released but rightly became a cult favorite pretty quickly. And it looks much better (natch) in the Criterion DVD than it ever did. It was filmed on a low budget and Robinson would be the first to tell you that the way it is shot is not the main reason to see it -- it is the script and the cast, and it's unforgettable.
Favorite scenes: The early moment in their squalid kitchen when they become terrified of their trashed sink; their first night in the cottage; Uncle Monty's home and his arrival in the cottage.