Over at the LiveJournal for "Tommy Westphall's Mind" (link to the left), RAF posted this comment:
This is kind of strange but it might count
Apparently a BBC sitcom called Spaced filmed a scene were one of the main characters met Dana Scully from the X-Files, however the scene was cut before the episode aired.
I know this is a long shot and I have never even seen Spaced so I have no idea what the context of the conversation would have been, but from what I have read the show sounds interesting.
I looked into this and found the following information at the IMDb.com:
The opening of episode 1.7 was originally intended to feature Tim having a conversation with a fictional character. Originally, this was intended to be Lara Croft, the heroine of the 'Tomb Raider' video game series, but the writers were not granted clearance to use the character. The scene was reworked to feature FBI agent Dana Scully of the TV show "The X Files" (1993) and the producers had even considered approaching Gillian Anderson, (Dana Scully), to fill the role, but the scene was eventually filmed with a lookalike. Writer and star 'Jessica Stevenson' was going to dub the voice of Scully, but the scene was cut and never completed.
Most other websites repeat that same information, so I don't think it even shows up as an extra or hidden feature on the DVD compilation. So as intriguing as it sounds, the crossover possibility fails to meet even the lax standards of Toobworld, let alone those of my Westphallian compadres who are strict disciplinarians. (But then they have to be, considering the premise that they're following.)