Black Books/WMG

Manny is the identical twin of Bilbo Bagshot from Spaced
Black Books and Spaced are proven to exist in the same universe, since in one episode, Manny is heard talking to Twist Morgan. Because of this, the only reasonable explanation for why Manny and Bill Bailey's character in Spaced, Bilbo Bagshot, look so similar, is that they are identical twins. Additionally, Evan, the manager of Goliath Books, is probably related to Tim Bisley.

It wasn't the replacement rose wine that killed the Pope.
It was one of the non-miraculous wines on the dusty shelf, which was inferior because it hadn't been rotated in seventy years and the bottler had spat in it. You don't give someone a literal miracle wine just for getting your cousin out of a minor assault charge, even if that someone is the Pope and the victim was a celebrity, especially since, well, the Pope... Wine made by the church from miracle grapes... It could be a bit insulting, and he probably wouldn't have wanted to risk it.

the doctor who treated Manny in the first episode was a young John Watson.
Another one of those 'actor's the same, so character is the same', but they're both doctors, and it's possible that John hadn't joined the military in 2000.
 * Makes sense, maybe he didn't think to join the army until we actually invaded Iraq/Afghanistan/I can't remember where John Watson actually got his limp.

Sherlock Holmes got his nice coat from the Oxfam shop Bernard donated to in the second episode.
If the above Guesser is right about the two shows taking place in the same universe then why not? Bernard loves dark clothes and big coats. He didn't necessarily get rid of his coat as part of that donation, but could be the same Oxfam shop.